Right click and select Color Picker, or hit CMD-SHIFT-C/CTRL-ALT-C to open it. Currently reads HEX, HEXa, RGB, RGBa, HSL, HSLa, HSV, HSVa, VEC3 and VEC4 colors – and is able to convert between the formats. It also inspects Sass and LESS color variables. Just open the Color Picker with the cursor at a variable and it'll look up the definition for you. From there, you can click the definition and go directly to where it's defined.