Is there a way i can turn every instance 0 to the text zero using the
custom formats option under format cells?

General;General;"zero"

Also is there a way to
change the colour of every piece of text in cells.

If you mean the color of the entire cell,
General;[Red]General;[Blue]"zero"
is an example of making negatives red and zeros blue.

I know how to make different parts of the text different colors if the cell
contains a literal text string constant, but not a formula and not a
number. Select a part of the text string and use
Format Cells Font Color
or an equivalent command button.

I have Excel 2003.