i think this will me a Katie answer for details- but its down to the way the combination of the eye colour genes (there are quite a few genes if i remember correctly- 6 or so?? ) from each of your parents are expressed.
Good question, this is a result of genetics, your genes control what you like like and are inherited from your parents.
There are actually up to 16 genes that control eye colour, but the basic explanation is that two genes primarily control whether you have blue or brown eyes (OCA2 and HERC2). These two genes need each other to work and control the amount of pigment in your eye.
If someone makes a lot of pigment in the front part of their eye, they have brown eyes. And if they make none there, they have blue. A working HERC2 is needed to turn on OCA2 and OCA2 helps to actually get the pigment made. They need each other to make pigment, so to have brown eyes, both genes need to be working perfectly, but to have blue eyes, one or both of the genes need to be ‘broken’.
You inherit these genes from your parents, and because the two genes depend on each other, it is possible for someone like you to have dark eyes and still have gotten your genes from your parents who have blue eyes (like your Mum). I’d imagine one of your Mum’s genes is working and the other is not, while both of your Dad’s are working. That meant you inherited one working copy of both genes from your Dad and your Mum. It’s possible that if you have any siblings that they could have blue or brown eyes!