Yes, the pressure force at the aqueous humor may cause the color change of iris which may change the color of eyes. Once our color of the eyes is changed, we should check out whether there is the problem at the body. Or else, it will not be changed. You'd better go to see the doctor and have a full check at the eyes. The eye color is generally determined by the genetic genes which is related with iris. It will not change easily. If you find the change at the color, like yellow, you may have the liver problems. Thus you should go to have a check.
There are several reasons that you will see stars when you are stretching. First of all, maybe it is because that you stand up very quickly, then the inertia in your body causes the blood to run out of your head and neck and upper body, thus making you see stars and in some cases some people may even faint. And the veins and arteries are strecthed a bit as well, and in doing that you increase the distance that blood has to travel around the body which means that again your brain gets less blood and you see stars. Besides, when you are stretching you rentire body, you are squeezing many muscles of your body at the same time, therefore, they all require oxygen, and this sudden requirement of oxygen by all the muscles being stretched will cause less oxygen to be available in the blood for the brain and hence you see stars. So, to avoid seeing stars or even faint, you can pay attention not to stand up too quickly. And notice that some foods which are good for blood can be added to your diet to help you keep in a normal blood pressure and keep fit.
While engaged in exercise or stretching, the flow to your brain and eyes may temporarily be limited. This can create visual disturbances, such as seeing spots, floaters or other strange visual phenomena. The situation should be temporary and the spots should go away once normal blood flow returns. Warming up by walking or jogging for five to 10 minutes before stretching may prevent you from seeing spots as the result of reduced blood flow.