The new Entertainment Weekly (Twilight cover) has Castle/Beckett featured on page 28 in the news style section. It's where readers write in asking on where to find something like makeup, clothes, etc … that the stars are wearing. Here's what it says:

I love the lipstick Kate Beckett wears on Castle! What color is it? – Vicki

With a rogue colleague like Castle (Nathan Fillion), it's no surprise that detective Beckett (Stana Katic) keeps the rest of her life simple. For her neutral look, makeup artist Debbie Zoller uses Laura Mercier's Hydra Tint SPF 15 lip balm in "Bronze Tint" (lauramercier.com; $20) topped with Bobbi Brown's Creamy Lip Color in "Honeysuckler" (bobbibrowncosmetics.com; $22).

Both have online commerce sites:

http://www.lauramercier.com

http://www.bobbibrowncosmetics.com

But both brands are readily available in department stores like Nordstroms, Bloomies, Neiman Marcus, etc. Laura Mercier is available also at Sephora.