For the subtype, I was thinking fire as well. That will automatically give it immunity to fire and vulnerability to cold.
Oddly, the black dragon retained its 2e breath weapon damage progression (2d4-24d4), yet the brass changed from 2d4-24d4 to 1d6-12d6. I suppose we can go either way with it.
Good catch on blinding hide. It should probably have a limited range. Maybe 10 feet per age category, beginning with young (30 ft.)?
Its 2e AC progression was the same as both black and white dragons. Now the black's natural armor bonus is 1 higher than the white at each age category. Shall we mimic the white?
Its spellcasting is quite potent...not as good as a gold, but better than silver, red, mercury, shadow, and steel (all among the best spellcasters in 2e). All of them now go from 1st to 19th beginning at young, so that's probably the best approach for the jacinth.
Since it could cast priest spells in 2E, we'll need to pick some domains. Fire seems a good fit, as does Trickery. Any suggestions for a third domain?
Its magic resistance progression followed the same as the brass in 2e, so perhaps we'll just follow the brass's spell resistance progression?
Its land speed matches the 2e black, green, and reds, which all have 40 feet in 3e. As a flyer, it falls between the topaz and crystal dragons and the black in speed, but has better maneuverability than all dragons I could find with 3E counterparts. So how about following the speed progression of the topaz, crystal, and black (all appear the same), with one maneuverability class better?
Class skills? Diplomacy and Sense Motive, the two most obvious choices, are already class skills for dragons. Maybe Appraise? Bluff?
For ability scores...
Its damage output is closest to the bronze dragon in 2E, so maybe we can use the Str progression of the bronze.
Nothing seems to indicate that their Dex is better or worse than most dragons, so 10's all the way should suffice.
Since they are hearty desert survivors, I'd assume Con is decent.
Int is on par with gold, amethyst, and sapphire dragons.
Wis should probably be slightly less than Int and Cha.
Cha should be decent due to their reliance on magic.