Yes there certainly is a way!
Go to 'Actions' -> Show action list -> type in "tweak" in the filter bar -> double-click on 'Theme development: Show theme tweak/configuration window'.
Now that this Theme tweaker has appeared, you type in "grid lines"in the filter bar.
You will see 5 grey boxes with the descriptions next to them. The ones you want are: Grid lines (start of measure), Grid lines (start of beats) and Grid lines (in between beats).
By clicking on those boxes you are given the option to colour them the way you want.
You can give them a darker shade of grey. Or give them a different colour for each one.
When you type in "Midi editor grid", you'll be able to do the same thing for your midi editor grid lines.
When you have made the changes, make sure to click 'Save Theme' in the Theme Tweaker. I usually give it a different name to keep the original theme stored as is.
I hope this helps. Good luck!