Crossfades looks bad

[Holm]

Hello,

I have a problem with cross-fades.
I would like to cross-fade the same image twice, with large colour areas in which the colour changes only with the colourize effect.
The result does not look good, perhaps like streaming with too little bandwidth.
The opacity seems to have a special influence. The lower it is, the worse it looks.
The duration of the cross-fade also has an effect.
Does anyone have any advice.
Thanks in advance

[Zoltán]

Some pictures on what you see would be great help trying to figure out what's going on.