Black in an amplifier does not boost the Bloodbound.
Quick test : field V3. G5 yellow + G5 Black + G1 Red = G6 YBR.
107-317 damage, range 6.8, 1.32 shots per sec, 7% x1.5 damage, 1.11 chain, x1.02 damage and specials (+0.016 per hit level) 0 hits. That's in a tower surrounded by empty amplifiers.
Using 1 G5 gem in an amplifier next to this tower :
Orange (not part of the gem combination)
118-340 damage, 7.4 range, 1.41 shots per sec, 7% x1.5, 1.11 chain, x1.02 damage and specials (+0.016 per hit level) 0 hits.
Yellow
118-348 damage, 7.4 range, 1.44 shots per sec, 7% x1.69, 1.11 chain, x1.02 damage and specials (+0.016 per hit level) 0 hits.
Red
124-346 damage, 7.4 range, 1.44 shots per sec, 7% x1.5, 1.2 chain, x1.02 damage and specials (+0.016 per hit level) 0 hits.
Black
118-355 damage, 7.4 range, 1.44 shots per sec, 7% x1.5, 1.11 chain, x1.02 damage and specials (+0.016 per hit level) 0 hits.
Black in an amplifier boosts damage and range more than anything else did, but it did nothing at all for the Bloodbound special.
Prior to 1.0.16 Pure Black was one of the better (sometimes the best, sometimes not, it was weird) choice for amps. Now, it is perhaps the worst choice, seeing as the main thing you want to boost is the specials.