Coming from a background in web we often use hex codes for setting color. This already works well while setting the color in sprite properties. You can currently enter a hex code in common properties/color for sprites.
Using Hex for expressions would also be a welcome addition.
rgbHex(FF00FF) - defaults to 100% opacity when the string length is 6 characters.
rgbHex(FF00FF80) - Sets the opacity to 50%, sets opacity when the string length is 8 characters.
Short Version is nice as well but not required.
rgbHex(F0F) = FF00FF
rgbHex(F0F8) = FF00FF88
Benefits of this format are that they are much more easy to copy and paste from various graphics software. Is usually easy to remember and when inserting you don't have to insert 3-4 different values... just 1.
Sprite editor only supports RGB and HSL so an option to enter hex code there as well would be good.
Hex color support in the Animations Editor is now supported in r138. (For any other suggestions please post them separately since they cannot be tracked individually if only mentioned here.)