Color picker problem

[GreenThunderBolt]

Being new to Photoshop, I'm having a problem. After selecting the exact shade of green that I need (R=127, G=225, and B=0), I select the brush tool and make a rectangle green. But when I use the eyedropper tool on my rectangle and open the color picker, I see that my rectangle is not the proper shade of green because the RGB values are not what I entered. Why?

 

[Rich54]

Try this experiment: after selecting your green shade (127,225,0) as the foreground color, instead of using the brush tool to fill your rectangle, try filling it by using Edit>Fill>Foreground Color. Then check the color with the eyedropper to see if it matches.

Assuming that works, the issue may have to do with your brush settings. Possibly your brush is not set to 100% opacity. Another possibility is that there are certain brush settings that allow the brush to automatically swap between the foreground and background colors.

It would also be helpful if you could attach your Photoshop file here containing an example of your mismatched greens.

 

[thebestcpu]

Hi @GreenThunderBolt
@Rich54 has a lot of good potentials of which could be going wrong.

Doing the Edit > Fill > Foreground would eliminate many of the potential pitfalls.

Some brush settings have a blending mode when you brush other than "Normal" which could paint a different color

However, one thing catches me pretty regularly and that is the settings on the eyedropper tool in the image below.
If the sample size is large, then if you place the eyedropper any where near another color, it will give you some sort of average among the two colors. If you want to eliminate that problem, set the eyedropper to point sample as well as the other settings pointed to by arrows.

Just another way to get the wrong answer and I agree it would help if you shared the file or screen shot of the problem
John Wheeler