Hot Sunlight & vibration. Try not marking plastic rails & trims on ugly caravan decks. Nightmare. I have blue food industry quality hose that is supposed to be "non-marking" This hose is just as bad as the black ones so don 't be tempted by them!!
It's not the hose that leaves the marks it is the cuffs that are close to the ends. I have found the single braid red hoses are best.