My grandson wants a stocking cap in Rasta colors; red, yellow and green. Anybody got any ideas for a yarn to use? Or a pattern? I’m new to caps so it has to be pretty simple.
Try looking up hats at www.knittingpatterncentral.com. Worsted weight yarn is probably the most simple to use. If you can use wool, I would use woolease by lionbrand.com, or look up on the patonsyarns.com or bernat.com for their basic worsted weight (“4” on the label) yarns. Both of the latter 2 companies also have acrylic worsted weight yarns, too. I mention these because they will have lots of colors and you should have no problem with getting those basic 3.
What type of fiber do you want to use?
Encore worsted has one of the most comprehensive list of colors of any yarn I know. Most yarn stores have it or it’s online. It’s machine washable and nice to knit with.
http://www.plymouthyarn.com/index.php?nav=cYarn.yarnDetail&yarnid=000055&searchcollection=000005
These can usually be gotten in craft stores-
Soft Acrylics - machine wash
http://www.patonsyarns.com/product.php?LGC=canadiana&SPP=999
http://www.coatsandclark.com/Products/KnittingCrochet/Yarns/Medium/Red+Heart+Soft+Yarn.htm
Wool - hand wash only
http://www.patonsyarns.com/product.php?LGC=classicwool&SPP=999
Are you on Ravelry? There are lots of easy stocking cap patterns on there. Does he want something floppy or something fitted? I just knitted two Felicity hats (pattern is free, PM me if you want the link) on a family trip and they are floppy and very easy to make. I have long curly hair and I was able to tuck my hair into the hats just fine.
If he wants something fitted there are several simple beanie patterns as well. Good luck with the hat. 
http://i-like-lemons.blogspot.com/2008/04/felicity-hat.html
this is the felicity hat.
'Rasta" colors are just the primzry colors. Cascade 220 and 220 superwash come in a wide variety of colors including primary and are both nice worsted weight hat yarns.
My youngest daughter will love that hat. It’s just bumped my next project.