If the OP goes down the route of Ilford filters but reads extensively about the yellow being lower contrastand magenta being higher contrast such as is the case on subtractive dichroic heads using single filtration then when using Ilford filters he shouldn't worry that the range of Ilford filters do not appear to be made that way, i.e. the grade 4, 4.5 and 5 filters are not progressively darker and more magenta which intuitively you might expect them to be.

So, in short, just ignore the colours on each filter. They work exactly as they should and even if the grade 5 filter appears lighter than say a grade 3 or even 3.5 it will give a higher contrast