The Regs. here basically allow any conductor to be sleeved at its termination points, except that a green/yellow wire may not be re-identified and used for any purpose other than earth.
The other way round it's illegal here too - a grounding conductor has to be permanently identified yellow/green along its entire length. However, cables without a yellow/green conductor are virtually non-existant except for large cross sections commonly used for services and other main line work. Those however, don't contain a ground wire, they're solely intended for TT systems ahead of the main grounding point (typically the local ground wire goes into the breaker panel, so any wiring between PoCo service box and main panel does not have a ground).
The only legal sleeving in Austria is re-identifying a grey conductor blue in a 4xxxmm2 cable (colors brown, black, grey, yellow/green) where a neutral is needed. 4x1,5mm2 and the like is highly uncommon anyway, so it does not happen that often - since it's so rare 5x1,5mm2 is usually cheaper just due to the great quantities sold.
