I've read the posts on conditional formatting for cell colour based on
another cell's value (eg. set the conditional formatting to "formula
is" and then "=A10" and set the colour as red / blue / whatever...),
however wondering if I can do this for an entire column without
individually changing the conditional formatting for each cell one by
one (as there are over 400 rows).

What I do is first apply conditional formatting to A1, then use the "Format
Painter" button to apply the CF to the column as a whole.

Format Painter is the command button that looks like a paint brush. Select
A1, click the command button, and click on the "A" header for the column.

As long as the cell references in the CF formula are relative, painting
adjusts them as it paints.