This applies to any EPs from PETS onward, people with Seasons have also experienced this behavior

If the accessories on your sims are flashing blue when you enter your lot, you can fix it for that session by doing a 'change appearance' on that sim. Just go to the mirror, your accessories will then look fine, and click ok.

Some users have had persistent problems and had to change appearance every time they went back to the lot.

Suggested fix:

Remove accessories from the Sims on the lot.
Save and quit.
Restart your computer.
Now come back into the game and you can put them back on the sim.

Another thing you can try is to delete the file 'accessories.cache' from your
My Documents/EA Games/The Sims 2


This particular problem does not happen for all pets owners, nor for all custom accessories, although we have not yet determined why this happens.