Change:
export const editorErrorBackground = registerColor('editorError.background', { dark: null, light: null, hcDark: null, hcLight: null }, nls.localize('editorError.background', 'Background color of error text in the editor. The color must not be opaque so as not to hide underlying decorations.'), true); export const editorErrorForeground = registerColor('editorError.foreground', { dark: '#F14C4C', light: '#E51400', hcDark: '#F48771', hcLight: '#B5200D' }, nls.localize('editorError.foreground', 'Foreground color of error squigglies in the editor.')); <del> export const editorErrorBorder = registerColor('editorError.border', { dark: null, light: null, hcDark: Color.fromHex('#E47777').transparent(0.8), hcLight: '#B5200D' }, nls.localize('errorBorder', 'Border color of error boxes in the editor.')); </del> <ins> export const editorErrorBorder = registerColor('editorError.border', { dark: null, light: null, hcDark: Color.fromHex('#E47777').transparent(0.8), hcLight: '#B5200D' }, nls.localize('errorBorder', 'If set, color of double underlines for errors in the editor.')); </ins> export const editorWarningBackground = registerColor('editorWarning.background', { dark: null, light: null, hcDark: null, hcLight: null }, nls.localize('editorWarning.background', 'Background color of warning text in the editor. The color must not be opaque so as not to hide underlying decorations.'), true); export const editorWarningForeground = registerColor('editorWarning.foreground', { dark: '#CCA700', light: '#BF8803', hcDark: '#FFD370', hcLight: '#895503' }, nls.localize('editorWarning.foreground', 'Foreground color of warning squigglies in the editor.')); <del> export const editorWarningBorder = registerColor('editorWarning.border', { dark: null, light: null, hcDark: Color.fromHex('#FFCC00').transparent(0.8), hcLight: Color.fromHex('#FFCC00').transparent(0.8) }, nls.localize('warningBorder', 'Border color of warning boxes in the editor.')); </del> <ins> export const editorWarningBorder = registerColor('editorWarning.border', { dark: null, light: null, hcDark: Color.fromHex('#FFCC00').transparent(0.8), hcLight: Color.fromHex('#FFCC00').transparent(0.8) }, nls.localize('warningBorder', 'If set, color of double underlines for warnings in the editor.')); </ins> export const editorInfoBackground = registerColor('editorInfo.background', { dark: null, light: null, hcDark: null, hcLight: null }, nls.localize('editorInfo.background', 'Background color of info text in the editor. The color must not be opaque so as not to hide underlying decorations.'), true); export const editorInfoForeground = registerColor('editorInfo.foreground', { dark: '#3794FF', light: '#1a85ff', hcDark: '#3794FF', hcLight: '#1a85ff' }, nls.localize('editorInfo.foreground', 'Foreground color of info squigglies in the editor.')); <del> export const editorInfoBorder = registerColor('editorInfo.border', { dark: null, light: null, hcDark: Color.fromHex('#3794FF').transparent(0.8), hcLight: '#292929' }, nls.localize('infoBorder', 'Border color of info boxes in the editor.')); </del> <ins> export const editorInfoBorder = registerColor('editorInfo.border', { dark: null, light: null, hcDark: Color.fromHex('#3794FF').transparent(0.8), hcLight: '#292929' }, nls.localize('infoBorder', 'If set, color of double underlines for infos in the editor.')); </ins> export const editorHintForeground = registerColor('editorHint.foreground', { dark: Color.fromHex('#eeeeee').transparent(0.7), light: '#6c6c6c', hcDark: null, hcLight: null }, nls.localize('editorHint.foreground', 'Foreground color of hint squigglies in the editor.')); <del> export const editorHintBorder = registerColor('editorHint.border', { dark: null, light: null, hcDark: Color.fromHex('#eeeeee').transparent(0.8), hcLight: '#292929' }, nls.localize('hintBorder', 'Border color of hint boxes in the editor.')); </del> <ins> export const editorHintBorder = registerColor('editorHint.border', { dark: null, light: null, hcDark: Color.fromHex('#eeeeee').transparent(0.8), hcLight: '#292929' }, nls.localize('hintBorder', 'If set, color of double underlines for hints in the editor.')); </ins> export const sashHoverBorder = registerColor('sash.hoverBorder', { dark: focusBorder, light: focusBorder, hcDark: focusBorder, hcLight: focusBorder }, nls.localize('sashActiveBorder', "Border color of active sashes."));

Discussion:
When I set this: <img width="194" alt="image" src="https://user-"I see this: <img width="71" alt="image" src="https://user-"I was expecting: ! Version: 1.78.0-insider (user setup) Commit: Date: 2023-03-31T01:47:17.818Z Electron: 19.1.11 Chromium: 102.0.5005.196 16.14.2 V8: 10.2.154.26-electron.0 OS: Windows_NT x64 10.0. Sandboxed: Yes
I don't know a lot about why this does a double underline. This color initially came in via
Looks like we didn't think much when choosing the name.
Should we iust change the description and leave the key name as is then?
It looks like the implemented fix just changes the description and still leaves VSCode with no way of drawing a nice, noticeable box around the errant code. This doesn't seem like a fix to me — just labelling it "it's not a bug, it's a feature". Ideally, the key name for this feature should be changed to (or similar) and should actually produce a border around the whole code. This seems to be what the OP wanted, and it's certainly what I want — I'm trying to migrate from RubyMine, and RubyMine can do this, and it's extremely helpful, as the underlines are too easy to miss, especially when the Stylelint plugin seems to only want to highlight the first character of a line and not the whole line. Please could we have a way of actually drawing a border around the whole of the code?
I would have liked a border, but that would be a new feature (not sure if there's an issue discussing this). The change just corrects the description to what it actually does, without changing the key which would break themes that already use it.
I understand where you're coming from with that, but I do wonder what the key would be for a border if is already taken for the underline. , perhaps? Cache invalidation and naming things
If we actually a border, I would guess we would just use the .border key there and add a new double underline one. Kind of a soft breaking change as opposed to a theme color just not getting used all together.