I often work out conditional formatting formulas by putting the formulas on the worksheet. So, to figure out if column B is less than column C, the formula would be

=B2<C2

The result is either TRUE or FALSE. If you plug that into a conditional format, then the TRUE will trigger the formatting. I'm not quite sure what you mean with
If column B is less then column C (due to the negatives), i want it to be coloured colour A.
There really is no room for interpretation. -1000 is smaller than -500. BECAUSE of the negatives.

The second formula would calculate if B is less than C + 35%, is that right? If so, something like this will work:

=B2<C2*1.35

Again, this will return TRUE or FALSE and can be used in a conditional format.

Now, in your data sample, the results of both formulas are the same for the first and the second condition. What formatting to you want to apply if BOTH conditions are true? Do you want to keep the formatting for the first condition and ignore the second condition? Or should the second condition override the first condition?

Please post a data sample with a few more numbers that show all the possible cases and manually color the cells as you would want to see them after the conditional format. Then we know what to aim for.