Add color

[Terkwood]

goal

Add color to the trees.

plan

See colormesh repo for an example of how you can alter the color of a mesh / spatialmaterial / image

• figure out how this impacts the cache layer -- should we cache alterations to the albedo color? ignoring the cache for the first pass of this effort would be nice.
• turtle-crab: allow other stroke colors
• update gen to use new turtle lib