Colors in drawings question

[fuggy]

It is important that 4 similar parts of the invention be different, but not specific colors.
I would like one part to be, say, color A another B another C and another D.

How do you mark that on your black and white drawings? I tried four different shade lines but adding even more lines to a line drawing muddies the system.
If I write "Color A" on the drawing and point a line to the part, it will look like the name of the part is "color A".

I do not wish to send in a color drawing because any specific color is not necessary.

Any advice you can give would be appreciated. I looked on a checkerboard pattent and the writer called that "two contrasting colors" but I have four different contrasting colors so I need a marking system.

[Jonathan]

Why is just stating in the spec that the 4 parts are each a differing color not sufficient? Your comments seem to indicate that each part can be sufficiently called out by a lead line - just assign a reference numeral to each part.

OTOH, if you really do want to further delineate those 4 parts, perhaps do a 2nd figure where nothing else is labeled but those 4 parts and you can then do your shadings. Maybe an exploded view could also work to add in the shading, depending on what you are dealing with. Another option could be a dis-assembled version with those 4 parts shaded differently. I don't know the specifics of your situation so perhaps these suggestions may not be useful - don't state the specifics of course, on here, but you know not to do that.