I have made a mosaique of the sun, but all pictures have different light levels. I was wondering how to match these colors to be the same everywhere.
So basically I need all the pink to be the same shade, so that it will look like one picture.
Ideally, you want to attempt something like this with a fixed set of camera settings and lots of overlap so you can avoid using any vignetted portion. To try and do it manually, you will need to account for white balance, black point, white point, gamma and any vignettes (such as on the lower center piece). If you don't have a known gradient for the vignette, it will be pretty time consuming to do.
Your best bet may actually be to overlap the layers and use an eraser brush with soft edges to help blend them together. You'll still have some variation, but it should make it less noticeable as the variations shift. If you don't have enough overlap, this technique won't really work either though.
So I fixed it by setting it to grayscale and doing levels then (a lot easier) and afterwards healing whats left with the heal brush.
You could use a professional stitching software that does this, or use some freeware, e.g. Panotools. Those automatically do the required steps (maybe after some manual help).
An alternative is to go to Lab, pick representative points on the perimeter of the sun, and use curves to manually arrive at the same luminance, "a" and "b" values. Then pick a Lab value for the center, and use further curving to adjust that point on each image, meanwhile leaving the previously set curve points on each layer untouched. You will at least have two points matching on each layer. You will still have to manually mess a bit with curves' curvature, but two points on each curve is a good start. You will probably need one more. You can use the black point as well, and use the symmetry point of the composite image abundantly.
And BTW: you will have to disconnect curves for L, "a" and "b" for each layer, at the beginning.