Horses with one copy of the pearl gene don't exhibit any changes on their coat, since this gene is recessive.
A horse with a bay base and two pearl genes (PrlPrl) however will have a diluted coat, being a golden yellowish color.
If a horse has cream and pearl (CRPrl), the pearl gene is expressed. In the case of a bay base the horse would be a buckskin pearl, having a cream colored coat, with a darker mane and tail.