Use Clean Installer to scan your Downloads folder.

Default replacements will have a type of 'replacement' so you can find any defaults easily to remove them.

The easiest method is to get Delphy's Download Organiser and use it to scan your downloads.

If your problem is caused by a default replacement skintone and you would like to find it in your downloads to remove it, here's how: If that does fix it, you can add it to your userstartup.cheat file. You have a bit of a lower-powered graphics card and you have the cheat boolProp useShaders true on - try bringing up the cheat console (CTRL-SHIFT-C) and type boolProp useShaders false and see if that fixes it.You have an improperly made default replacement skintone that does not properly replace all skintone files, so it's left out some and is causing that mismatch.You have more than one default replacement skintone, and they are conflicting, causing the error you see there.

If you are getting a problem that looks like this picture, your problem is probably one of the following:

Sims 4 default skin replacement