Starscream doesn't seek Milly out necessarily, but being in the same vicinity, it's sort of inevitable that one of them will at least see the other, whether they end up engaging or not.

He catches sight of Milly when he's walking back to the group from harassing Orion, and at first he feels a thrill of cruel amusement. He'll have to point her out to Knock Out, he thinks; perhaps they can scheme something horrible up.

Then it occurs to him that he used this avatar as bait to confront her that one time and swiftly begins to panic. He needs to adjust his appearance, immediately, before it's too late--

When he's certain no one is looking, he changes his hair color to jet black and his suit to a slightly darker grey. Genius.