Let users choose their own colors

When planning sprints with the physical board, we generally prefer this or that color (I'm red, for example). We should be able to choose these colors. It's also inconvenient when two automatically chosen colors are very close to one another (right now, Gerald and I are two very similar shades of pink).

Start by examining how the board currently assigns and displays user colors. Determine where color preferences could be selected and stored, and how similar automatically chosen colors are handled. Done means users can choose their own colors and the board remains usable when multiple people choose or receive similar colors.

Written by the indexing model from the issue text.