Numbers negative values

This question might need a Numbers Whizz to answer. I have a large spreadsheet and in some columns where the calculation is a negative number in sterling I get what I want to see which is a minus followed by the pound sterling sign and then the value. Clearly any positive calculation is in black text so it is easy to see at a glance what is positive and what is a negative value. What I do not understand is that I also have calculations in the same sheet where the negative sterling value is all in black so it is a black minus sign black pound sterling sign and black value. If I go to the Cell tab and select Currency I am given the option, alongside the number of decimals I want, of two choices for negative numbers which are red. One is just the value in red and the other is the value in brackets in red. Can someone tell me why I am not given the option of a minus sign followed by the currency symbol and the value all in red so that all negative numbers in the sheet are consistent in style ? Thanks.