Don't feel stupid for asking, it's perfectly fine!
I downloaded the Electric Blue water, as well as the purple one, and did the exact same thing as you. I put the image in Textures and the .material in the Materials folder. It seems to be working for me, odd it isn't for you.
It's possible you may just be typing in the name wrong. It's case sensitive so make sure you're including capitals and any spaces in the name.
I opened the .material file with Notepad for both and this is what needs to be typed in Map Maker:
ElectricBlue and
PurpleWater. Try typing in either these two and see if it works.