A variation of this recipe calls for a grapefruit instead of an Orange. I've used it in the past and prefer a pink grapefruit as the standard ones impart a slight bitter taste which requires more sugar to mask.
*Marmalade is a fruit preserve, made from orange or other citrus fruit, sugar, and water. Some recipes include some amount of peel and zest, which imparts a sharp, bitter taste from the bitter citrus oil.
NOTES ON LEMON MARMALADE: This takes less than 2 hours to make. It's incredibly tart so don't skimp on the sugar.