var clr : int
var r, g, b : real
var rdiff, gdiff, bdiff := 0.005
r := 0
g := .5
b := 1
loop
    if r + rdiff > 1 or r + rdiff < 0 then
        rdiff := -rdiff
    end if
    r := r + rdiff
    if g + gdiff > 1 or g + gdiff < 0 then
        gdiff := -gdiff
    end if
    g := g + gdiff
    if b + bdiff > 1 or b + bdiff < 0 then
        bdiff := -bdiff
    end if
    b := b + bdiff
    clr := RGB.AddColor (r, g, b)
    colorback (clr)
    cls
    locate ((maxrow div 2) - 1, maxcol div 2)
    color (white)
    put whatdotcolor (5, 5)
    delay (50)
end loop