Get Color of a pixel in RenderTexture

Hi, I have RenderTexture where are rendered some sprites and I want to color of a some pixel in RenderTexture.

is there any way to get pixel color in RenderTexture?

this works on a whole scene but I need it to be pointed only to my RenderTexture.

     glReadPixels(pos.x, pos.y, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

Please refer to Synchronous glReadPixel in cocos2d-x-v3