Ok i Solved the problem by using CustomCommand:
auto pixelPos = CC_POINT_POINTS_TO_PIXELS(center);
cmd = new CustomCommand();
cmd->func = [=]() {
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glReadPixels(pixelPos.x, pixelPos.y, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, pixel);
};
rt->beginWithClear(0, 0, 0, 0);
spr1->visit();
_director->getRenderer()->addCommand(cmd);
rt->end();