Some of the Corn Island Boas do not darken much when mature.
Some lines of Cay Caulkers stay light silvery grey into adulthood.
The Hypo Sonorans stay fairly light silvery with lots of pink.
Some lines of Hoggs stay relatively small (4-5'max) and the best of the best will stay light and clean.
Some of the Nicaraguans stay fairly light and/or clean. I know I held back about 10 or more from last year that look pastelish, ghost'ish or hypo.
Some lines of Cancun Boas stay light and vibrant into maturity. I know the Cancuns i've bought from Gus at Rio Bravo Reptiles look like some ultra colorful hogs.. light and sweet.
The Hondurans and Costa Ricans are also very variable and some will remain light tan into adulthood, rather than turning Olive or Grey.
Keep your eyes peeled for these treats!
Hope that helped...
Take care, Joe Rollo - Bci Joe

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Thanks and take care - Joe Rollo
'Tis not the stongest of the species that will eventually survive, nor the most intelligent, but the one most responsive to change' Charles Darwin