Matched the color but color changed

DLau

I finished a painting with a green wall but the longer i look at it there is a spot that the value is off.  I decided to mix a new paint to retouch it.  I was proud of myself that the retouch paint match perfectly. it was seamless. BUT after a week, the retouch paint area turn darker. Now, I'm afraid to do anything.

Question: How to retouch a painting?

dencal

DLau

Does it matter? Value variations add interest.

Glaze over the spot, blending into the adjacent Green values.
Premix sufficient paint and redo the whole wall.
Select stable pigments that don’t shift when dry. Are you using student grade paint?

Denis

Richard_P

Is this in oils?

Is the new patch more matte than the shine of the old paint? Gloss can affect value.

DLau

That is a good question.  I got tunnel vision just want to fix the problem. I should have repaint the whole wall.  Thanks
For the sake of understanding.  If I mix the new paint to match the old paint seamlessly implies there are two identical pigment content. If it shift should they shift the same.  I use Geneva paint.

It is not the gloss. I look at it at different angle and block any glare.  

DLau

I think I can answer my own question.  I matched the already shifted color so therefore, when the new color is dried. it is darker.

Richard_P

What might work is if you apply gamvar over a small area of the dried paint, and if the colour is different than the unvarnish area then colour match against this colour before applying again. You can remove gamvar with gamsol once you've done this.

DLau

Thanks Richard_P and dencal for your suggestions

hassibnoorial

Before retouching, you should have oiled in the painted part and then mixed your color. 
The problem is, when oil paint dries, all the oil sunks by the surface of the canvas and the color loses contrast. To bring the original color back, you must oil in the surface and then start making changes with your next layer.