"A bheil falt ruadh ort?"
Translation:Do you have red hair?
It's not just about the colour. Ruadh is the old word and is usually used for natural things - unless they are really scarlet like a strawberry. The original sense of dearg was actually 'altered, adulterated', before it became a colour. It is related to English dark. You will meet it in expressions that have nothing to do with colour, always in a negative sense, and it was used to distinguish the part of the field that you have ploughed from the part you have not yet ploughed yet (bàn). So almost all plants and animals that have red in the name are ruadh in Gaelic.