What does scale look like?

For water, I use something like what Jim recommends normally: mostly RO
water with some filtered tap water, and I flush the boiler around once a

Today I descaled following Jim' directions. I got quite a bit of greenish
tint, as Jim warns comes from the copper boiler, but I couldn't see anything
else in the water. Should I see scale? What would it look like?

The part that worries me is that I also descaled the HX. Jim recommends
about six flushes, about two minutes apart. I got a phone call during the
process, and let the last interval be around 40 minutes. The water I'm
flushing from the brew head definitely has stuff in it: they are black
flecks that sparkle silvery in sunlight. What are they? Did I screw up?