I had a clear 11x that was kinda yellowed. It didnt take yellow/pink very well and red looked really dark. There is not really a color IMO to make this brighter as the plastic is older.
I had a tye dye disc that was hard as hell to see. I slapped a black stencil on the middle and its better but still not great.
If it where me I would dye it all yellow or red taking into consideration that it might be duller than you like. If you go with red or similar I would suggest to mask off the blue/green/purple as these will just get darker.