If you just want to see the colors in action, here's some some JavaScript you could run with Deno:

    const encoder = new TextEncoder();

    function csi(text, ... args) {
        const filt = args.filter(xx => xx !== null);
        const output = "\x1b[" + filt.join(";") + "m" + text;
        Deno.stdout.writeSync(encoder.encode(output));
    }

    csi("True Color RGB:\n");
    for (let ii = 0; ii<32; ++ii) {
        for (let jj = 0; jj<64; ++jj) {
            const fg_rr = jj*4;
            const fg_bb = ii*8;
            const fg_gg = (fg_rr + 3*fg_bb)>>2;

            const bg_rr = 255 - ii*8;
            const bg_gg = 127;
            const bg_bb = 255 - jj*4;
            csi("+",
                38, 2, fg_rr, fg_gg, fg_bb,
                48, 2, bg_rr, bg_gg, bg_bb,
            );
        }
        csi("\n");
    }