A method for presenting information includes receiving a specified digital value for display, assigning to a set of colors respective digital codes comprising respective binary values representing three primary color components of the colors, and encoding the specified digital value by combining at least four of the digital codes while selecting the colors such that none of the binary values is constant over all of the selected colors. A symbol is presented for imaging by a computing device, the symbol comprising at least four regions meeting at a common vertex and having the colors selected so as to encode the specified digital value using the respective digital codes.