• Create image from code (color picker)

float w = ofGetWidth();
float h = ofGetHeight();
float cx = w/2;
float cy = h/2;
 
img.allocate(w,h,OF_IMAGE_COLOR);
 
for (float y=0; y<h; y++) {
    for (float x=0; x<w; x++) {
 
        float angle = atan2(y-cy,x-cy)+PI;
        float dist = ofDist(x,y,cx,cy);
        float hue = angle/TWO_PI*255;
        float sat = ofMap(dist,0,w/4,0,255,true);
        float bri = ofMap(dist,w/4,w/2,255,0,true);
 
        img.setColor(x,y,ofColor::fromHsb(hue,sat,bri));
    }
}
 
img.reloadTexture();  

• Get color from an image:

ofColor ofxGetPixelColor(ofBaseHasPixels &img, int x, int y, int w, int h, int bpp=3) {
    ofColor c;
    int i = y*w*bpp + x*bpp;
    c.r = img.getPixels()[i+0];
    c.g = img.getPixels()[i+1];
    c.b = img.getPixels()[i+2];
    if (bpp==4) c.a = img.getPixels()[i+3];
    return c;
}
 
ofColor ofxGetPixelColor(int x, int y) {
    ofImage img;
    img.grabScreen(x,y,1,1);
    return ofxGetPixelColor(img,0,0,1,1);
}

• Juego con rangos de colores

ofBackground( 255, 255, 255 );
// Rango de negro a rojo
for ( int i=0; i<256; i++ ) {
	ofColor color = ofColor::red;
	color.setBrightness( i );
	ofSetColor( color );
	ofLine( i, 0, i, 50 );
}
// Rango de blanco a rojo
for ( int i=0; i<256; i++ ) {
	ofColor color = ofColor::red;
	color.setSaturation( i );
	ofSetColor( color );
	ofLine( i, 80, i, 130 );
}
// Toda escala de colores
for ( int i=0; i<256; i++ ) {
	ofColor color = ofColor::red;
	color.setHue( i );
	ofSetColor( color );
	ofLine( i, 160, i, 210 );
}