One of the following must be true:
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They're compressed (compression existed in Windows 7 as well).
Have you tried disabling the Compressed files and folders checkbox in Preferences / Display / Colors and Fonts / Files and folders - Compressed (shown in the FAQ I linked) and clicking Apply? That's the quickest way to test whether or not it involves compression.
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It's also possible they have the System + Hidden attributes set.
That's more red than pink, assuming the default colors, but hidden files are slightly washed out which can make System + Hidden files look a little pink. It'd be unusual for mp3s to be flagged as system files, but I've seen it happen.
That comes from Preferences / Display / Colors and Fonts / Files and folders - System.
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Or you've applied a label in Opus that changes their colors.
Labels can be applied to individual files, and can be reset via the menu shown in Set File & Folder Colors/Labels via Context Menu.
But if even a brand new *.mp3 file is a different color then it might be a label matching *.mp3 or similar, which you'd find under Preferences / Favorites and Recent / Label Assignments. (None exist by default.)
Label colors are defined under Preferences / Favorites and Recent / Labels.