Adding option for default color

[Bond246]

Hello,

big thanks for this project. It is lightweight and feature rich to work with it really well.

One option we would like to change would be to set a default color as ENV or define a specific color as URL-parameter.
Actually the board chooses a random color. In our usecase it would be easier just to have black default color on board-startup or to set a color via URL-Parameter.

Hopefully it is not a big thing.

Thanks,
Florian

[lovasoa]

PR welcome !