step-tuple (See related posts)

step-tuple: func [
    val [tuple!]
    /by step [tuple!]
][
    if any [
        3 <> length? val ; can only step values of 3 segments
        val = 255.255.255
    ] [make error! "Can't step tuple value"]
    either step [
        either (val + step) <> val [val + step] [
            make error! "Can't step tuple value"
        ]
    ][
        steps: [0.0.1 0.1.0 1.0.0]
        for i 3 1 -1 [
            either val/:i = 255 [val/:i: 0] [
                return val + first steps
            ]
            steps: next steps
        ]
    ]
]
; foreach val [
;     0.0.0 0.0.255
;     0.1.0 0.255.0 0.255.255
;     1.0.0 0.255.255
;     254.255.255 255.255.254
;     255.254.255 254.255.255
; ][
;     print [val tab step-tuple val]
; ]
; print attempt [step-tuple 255.255.255]
; print attempt [step-tuple 255.255.255.0]