Unknown bugs populating brussel sprout leaf

How about just posting a still picture that actually has some detail? The video is useless.

Some sort of aphid. They'll be getting inside the sprouts eventually, probably also encouraging a black mold due to their excrement.

That's what I thought it might be but these didn't have the characteristic green color. Upon closer examination they appear to have some sort of greyish coat that can be rubbed off to reveal the characteristic green of aphids that I'm used to. It may be the cooler weather is inducing them to produce some sort of insulation. I don't know that much about aphids.

I do know that ants defend them from predators so I'm go> James A. Bowery said:

Aphids come in a range of colors, including bright scarlet and black--some species even appear wooly white.

(I know that aphids are called 'green flies' in the UK, and I'm now wrapping my mind around 'red green flies.')