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Tartrazine
use a red dye on a yellow dye to get orange dye
Saffron is used to dye fabrics yellow. There are also some synthetic dyes which are used because saffron is very expensive.
primuline
Yellow
I'm assuming you were trying to ask the question, "How do I make yellow dye?", because there's no such thing as yellow food dye in runescape--you can't dye the food in there. Two onions and 5 coins, given to the witch Aggie in Draynor, will produce yellow dye.
Yellow dye number 5 is considered dangerous for human consumption. It has been proven that yellow dye number 5 is carcinogenic.
Red and Yellow dye.
Orange dye is made by combining a yellow dye and a red dye.
Orange dye can be made by putting yellow dye (from crafting yellow flowers) and red dye (from crafting red flowers) on the crafting table.
You need orange dye and blue dye. Aggie in Draynor Village can make red, yellow and blue dye. Combine the red and yellow to make orange dye.
To get Orange dye, you need to purchase or obtain Red dye and Yellow dye, and use one on the other.