If you're creating a post that is primarily for online distribution, you need to know what color gamut it will be distributed in. However, if you're creating a project that will be primarily or exclusively printed, then your primary concern is what color profile the printer requires.   To answer this question, we have to understand how color spaces work. A color space defines the range of colors that can be reproduced on a device. It does not necessarily define the range of colors visible in real life, but it does help determine how accurate or close to reality an image will appear when viewed on different devices. The two most popular color spaces are sRGB and Adobe RGB (1998). sRGB was created for web-ready applications designed for the online distribution and has become standard for digital design since then.