Here's the reason, as far as I can tell: There is no standard for what chemicals people use to colorize the BLACK ABS, and so not only is each vendor likely to use different chemicals, different batches from the same vendor may have different chemicals as they experiment with their processes to reduce cost and/or get their desired output. Different chemical composition (even just the coloring elements) means different material characteristics, including time and temperature variables related to getting the material to melt, flow, and set up.

Black ABS has proven the most challenging material to get the recipes dialed in for.

White ABS has been the second most challenging, probably for the same reasons as the black.

Pink, Red, Orange, Yellow, Green, Blue and Purple ABS - all fine.

Haven't tried any Grey ABS yet.

NOTE: also, check the thickness with calipers. We have seen material advertized as 1.75mm ranging from 1.60 to 1.80, and that can really throw off your flow calculations.