RGB (Red, Green, Blue) is the color protocol in almost all electronic viewing devices. The model is based on the way the human eye perceives color. There is no set standard for any of the three colors so the display of color images is device dependent. That is why it is important to calibrate equipment if we print photos and why our posted images might look different than how we thought they might look.
RGB is an additive model, the theory being that any color can be created by an additive combination of these colors. In contrast, most printers use a CMYK (cyan, magenta, yellow, black or “Key”) process which is subtractive; colors are made by subtracting from black. This is why getting a print just right can take some effort.
Here is my homage to red, green, and blue. All of the pictures were taken within a couple of hundred yards of each others. The alley window and wall were really this mellow blue, enhanced only by the morning light and shadows.