The one and only (sort of permanent) red dye used for plant/wood histology as a stain is Saffranin O.
I can't recall the Color Index number. It is both water and alcohol soluble. I never needed to use it in more than a 1% concentration. I have no idea how well it would perform at, say, 5%.
Baskets of wood sections or digests soaked for 2-3 hours as the very first step in the microscope slide preparation, counter stained with Fast Green FCF and differentiated with Orange G (just in case you run across the process). My wood species slides seem to look as good now as when they were made back in the late 1960's.
See if you can visit some university botany research lab. They might enjoy the puzzle, I know that I would have!
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