If you want to replace the color set in a multiplayer game without anybody having to rejoin:
1. Modify it with setColorTable or setSprayCanColors.
2. For all %clients that have reached phase 3 of loading: %client.transmitStaticBrickData();
3. For all %clients that have spawned: commandToClient(%client, 'PlayGui_LoadPaint');
If you want to go all the way, modify the spray can datablocks and transmit datablocks so that the particles have the new colors as well.
If you want bricks to update color in real time, set each brick to another color and immediately set it back to the original to let clients update it.