Allow transparent color in color input, allow removing color and impr…

[correct-horse-battery-bench]

…ove contrast of text above color in input

• Allow transparent color / no color in the color input component, use null instead of empty string
• allow setting defaultColor or random color as default
• display dark color on light color and light text on dark color inside the color input -> improved contrast
• allow removing the color when selected once

[correct-horse-battery-bench]

Looking at modifying the backend first so no color -> passes null instead of empty string.