Blender has some internal maps, to help you layout UV-maps.
I used one of them to do this challenge.
I’m not sure if I have that one handy, but I have a few others I’ve used over the years. These are very good for making sure the mapping is done correctly.
When, in Blender, creating a new image. You can choose for a blank version. Or this default texture. There is also a second type. No need for creating one.
I’ll have to check that out. I didn’t make any of the ones I have. I think I downloaded them all from one place or another online.
Oh, I just had a thought. I haven’t upgraded to 2.8 yet, so it’s possible these aren’t offered in 2.79. I’ll have to check that out. I’m definitely going to make a note in my ongoing 2.8 list for when I do get to install and use 2.8.
Edited to Add: YES, 2.79 has it, and another UV Grid option. Cool.