Priority: Low

Cosmetic Problem
In the Minecraft: Java Edition section of the Minecraft Launcher, under Skins tab, the two default skins (Alex and Steve) have still-image Previews of what the skin looks like under the name of the skin. Alex's still-image Preview is inaccurate to the appearance of the skin.

In the Skins Library, the default still-image preview for Alex is not only discolored in some areas, but there is some additional detail on the shoes that is missing on the actual Alex skin.

(The trim on the collar and sleeves of the shirt has a much lighter tan-green discoloration, compared to the darker green on the preview. The pants seem to have lost some contrast in the actual skin. The front end of Alex's shoes even seems to have lost some detailing: whereas in the still-image preview there is more shading/highlighting, the actual skin just has a plaid-like rectangular shape. Further scrutiny can show that there are some other less noticeable changes to the detailing, such as in Alex's hair, skin, and the shading on her shirt.)

How To View For Yourself:
Head to the Skins section and click the button marked "New skin" with the plus sign. Set the Player Model to Slim, and click Save without uploading any skin file. You now have a skin called <unnamed skin> in addition to your Alex and Steve (and any others you may have). The still-image preview generated under <unnamed skin> will be accurate to how Alex actually appears in-game. Compare that to the still-image preview under Alex and note the differences mentioned above.

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On a side note, the still-image skin preview for Alex actually appears to be unique; it's different from her official Java skin or Bedrock Skin (which is just the Java version but with low shoulders), and even Dungeons skin (which retains the lighter collar/sleeves tan-green, but has a third distinct version of her shoe shading that appears unrelated to either). I can't actually find the inaccurate version of Alex's skin anywhere else online, though I haven't been looking long.

The three attached images should show: Alex as the skin appears under Custom, along with the two <unnamed skin> and default Alex; zoom-in on <unnamed skin> and Alex as they appear in the Launcher; and an edited image which is meant to be a side-by-side closeup of the difference in the two (both faded gray because they are unhighlighted/unselected). 
[Edit: added non-grayed out versions, but the buttons appearing above them make some of the differences harder to see, others not: the shirt color itself is actually slightly different, too.]