If you click inside that outline with the selection tool, do you see a face selected? If not, there’s your explanation: you need a face to paint a material on it. But there are multiple things that could cause no face to form, and we can’t tell from an image which might be happening. Can you upload your skp file so one of us can take a look?
test.skp (658.6 KB)
No face selected after clicking inside the walkway. Thank you
No face to select.
Turn on Hidden Geometry and delete the unneeded edges first.
Before your model gets more complex it would be a good thing to learn about correctly using groups and components to separate geometry and also learn about proper use a tags. ALL edges and faces should be created and left untagged. Only groups and components get tags. Here I’ve correct the incorrect tag usage.
Thanks for pointing that out to me! I will research how to use groups and components. Do you happen to have any links or resources where I can learn about this? Thank you
Start with learn.sketchup.com