- You must add red, green, blue and yellow light bulbs to the grid to satisfy these rules.
- Each white hex must contain either a red, green, blue or yellow light bulb.
- Light bulbs of the same color cannot be in neighboring hexes.
- Each white hex must be lit by all four colors of light. This includes those that started with lights.
- Light travels away from light bulbs in six rays, one each through the six sides of the hex.
- Light continues in a straight line until it is blocked by a black wall hex.
With some trial and error, I managed to get the answer (in about an hour):
I am also able to confirm the uniqueness of the answer. A very high quality puzzle.
A brief description of my method:
I start with some obvious ones, such as one cell neighbored by three different colors.
Then I managed to find some other logical implications, such as in the "thin" areas, if we have two quadruples that have three cells in common, then the two "outer" cells must be equal, etc.
Some logical steps are more complicated, but everything is reasonable and does not require very deep logic.
Also technically, I keep a different layer, marking which cell has already got four colors. This makes it easier to check the cells.