My dopest hack. I have no idea how to use openFrameworks, but this will get the pixels from your screen and then give you back the rgb value of wherever you are clicking...

RGBFromPixel

void testApp::mousePressed(int x, int y, int button) {
    receivedImage = FALSE;
    ofImage theScreen; //declare variable
    theScreen.grabScreen(0,0,1024,768); //grab at 0,0 a rect of 1024x768. Equivalent to loadPixels();
    const ofPixelsRef pixels= theScreen.getPixelsRef();
    ofLog() << (int)pixels.getColor(x,y).r << ", " << (int)pixels.getColor(x,y).g << ", " << (int)pixels.getColor(x,y).b;
    
    ofxOscMessage m;
    m.setAddress("/color");
    m.addStringArg(ofToString((int)pixels.getColor(x,y).r) +","+ ofToString((int)pixels.getColor(x,y).g) +","+ ofToString((int)pixels.getColor(x,y).b));
    sender.sendMessage(m);
}