Kim Kardashian to OPI Nail Polish -- My Sisters Deserve Equal Pay

All Kardashian women may not be created equal ... but one of the biggest nail polish companies on the planet is sure paying them like they are ... and get this -- even the half-sisters are raking in BIG MONEY.

TMZ has learned ... all 6 K-ladies (Kris, Kim, Kourtney, Khloe, Kylie and Kendall) inked a deal with OPI back in March to become spokeswomen for a Kardashian line of nail polish ... featuring colors like:

Sealed with a Kris -- an intense dark red tone
Kim-pletely In Love – a soft, delicate pale pink hue
Khloe Had a Little Lam-Lam – an eye-catching dark emerald hue
Listen to Your Momager! – a striking deep blue tone

According to the contract, obtained by TMZ, the family was guaranteed $600,000 up front -- plus a cut of the nail polish profits.

Here's the thing ... the documents show the money is being divided EQUALLY between all of the women -- that's $100k-per-gal for all you math wizards out there.

Shocking considering Kim is in her own stratosphere when it comes to star-power ... then again, they say charity starts in the home.