simple jitter op question

Abao's icon

HI all
I am having this embarrassing problem... can anyone tell me why I can not have proper jpeg export after jit.op mixing? (exported file looks different then it looks in pwindow)
I simply mix 3 matrixes and it only results good on single plane image export, not working with full color, please help... (see the attached file!)
or is there a inner graphic setting for this issue??

many thanks