Minor fix

* 8byte hex color
* Reused pattern
* Dec value limitation
Add desc for functions
Make sure hex is 2 digit
Remove trailing char in result
New :Color command to keep original color format
Keep alpha value
Fix percent value accuracy
Reduce logic
Default color set to white
Improve 256 <-> 65535 conversion
Merge pull request #5 from othree/simplecmd

:Color for modify current color, and keep format