I'm talking about team's guernsey choices. As in, you need a clash guernsey which is dark if you have a light primary guernsey, and vice versa. As in GC couldn't have a blue clash in lieu of their white clash due to having a dark (red) home guernsey and also a dark (red) away guernsey. Maybe if they had a blue away guernsey and a white clash, or vice versa, they could wear the combo you suggestedEssendon and Melbourne using red WITH a dark colour was classified as a dark colour. Sydney was never affected.
Bulldogs currently wear this vs West Coast.
Teams use a white clash as it stops any issues with anyone they clash with (eg Crows thought about a yellow one but they'd still need something else for Eagles games).