Adult Color books, what kind of colors?

I have a 72 pack of Derwent pencils, my pride and joy. Even with 72 colours there are still not enough pinks and purples for my liking. 

I like Crayola brand, and 50 sounds like a decent amount of colours (possible lack of pink and purple notwithstanding!   ).

I like gel pens. Costco has a set of 100 for around $17. I also have colored pencils that were part of my birthday gift from an awesome pea.

I hate Crayola. Staedtler is so much better.

So the pens work well? I haven't I jutried them yet. I've been using belly roll ones but those are expensive even with a 40% off coupon at Michaels. I like the texture of pens better. Then again I use to do my math homework in pen because I don't like pencils.

I love the Prismacolor pencils. they blend well and then I add just about any other brand of colored pencils sets I can find. Right now I believe I have around 12 sets of off brands to supplement the Prismacolors since they are cheaper. It gives me a variation of reds, pinks, blues, etc without having to spend a fortune. The thing about Prismacolors is you can purchase one pencil at a time if you find yourself lacking a particular hue. Also, Prismacolors have a very intense color and can be used very dark.

Another vote for prismacolcors. I absolutely love them! Originally bought them for coloring black and white photos I was taking and developing myself. Now.... They're used for everything! You can use them like water colors too by using odor free mineral spirits and a blending stump.

i have set of fine tip sharpies and ultra-fine point sharpies. that way i have wider tip for bigger areas and finer tip for more detailed work. colours are nice and deep, just need to be sure when i printed the page off the internet, i used thicker card stock so it doesn't bleed thru.

Prismacolor, Derwent and Faber Castell's polychromos are all wonderful pencils; BUT they are expensive.  They may well be beyond the budget you are looking to spend for this gift.

I color with various mediums, including the above, but in your situation, I think a nice, but more reasonable alternative, is a box of 50 Crayola Coloring pencils (which I use as well as the expensive ones).  If you wish to give something more, add a 24 pack of Sharpies (either fine or ultra fine).