I came across an issue with composed looks recently which I couldn’t for the life of me find the fix searching on the web.
When you create custom composed looks in a subsite in SharePoint 2013 with a custom master page I couldn’t get the composed look to show up in the Change the look page. Even with using the OOTB master page I couldn’t get it to work. Bear in mind that the list was overwritten when we deployed a custom solution with an updated Composed look list.
After a little investigation I found the issue. While using a custom master page I was setting the url to the root site as this is where I assumed the master page was. I was wrong in a way. The subsite has it’s own master page gallery which is hidden. If you click the master page gallery it takes you to the root site but there is a hidden one on the subsite. If you copy the last part of the url for the master page gallery on your site (/_catalogs/masterpage/Forms/AllItems.aspx) and add it to the end of your subsite you’ll open the hidden master page gallery. Place you master pages in here and point the master page url to these. Voila you’ll now be able to see the Theme in the change the look page.
You don’t need to do this for the spcolor file, this can still be solely located on the root site.