Yellow dye number 5 is considered dangerous for human consumption. It has been proven that yellow dye number 5 is carcinogenic.
It is possible that the dye in mac and cheese is dangerous to your health. Yellow No. 5 has been connected to hyperactivity, asthma, some skin conditions and cancer. There have been no large scale studies that prove this, however.
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.
Have you tried tartrazine dye (FD&C Yellow 5).
use a red dye on a yellow dye to get orange dye
To make orange dye, get 3 onions, and 5 coins for yellow dye. then get 3 redberries, and another five coins for red dye. go to the witch in draynor village and make the dyes, then mix the yellow and red dyes
Yellow
Red and Yellow dye.
Orange dye is made by combining a yellow dye and a red dye.
yellow stool dye #5
Gorbet Shuo
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.