Cut the rhubarb into small chunks and put into a pan. Add the orange juice (or water) and sugar and simmer gently, covered, for 10 minutes until soft. Leave to cool.
Add the custard and yogurt to the rhubarb and gently fold together. If you want to keep the different swirls of colour from the pink rhubarb, yellow custard and white yogurt, then barely mix together. Alternatively, blend everything together to form a pale pink dessert.