Hasta La Motion!

I am new to Nuke 5, and I wanted to ask you if there is a node/CC node where I can manage to make the white-greeny circle around the blue mat the same blue color. I need it, of course, for a sequence. I tried to make a luma matte from the r or g channel, but bad pixel appeared and its not 100% covering the white-greeny spot.
I don´t want to mask the little circle all 100 frames, maybe there is a method in Nuke I am not aware of? I tried the hue-shift but it didn´t work well for me 🙁

The picture tga is as attachment (sorry I cannot show anymore, just the cropped one).

Thank you very much in advance!