I have made a few attempts so create sugar glass.  It yellowed each time.  What am I doing wrong?  Ugh! so frustrating!  One tip I read said that my thermometer might be off.  I am going to calibrate it and try again.   Any other suggestions?!

Well, your thermometer could be off, but when you get to 300F, your gonna start getting color.  

Couple things, try cooking it faster.  The longer it takes to get to temp, the more of the sucrose will break down and cause yellowing.

Corn syrup could be added.  A lot of hard candies use it to help keep it clear.

I would suggest trying isomalt if you really want an easy way to make it.  It doesn't attract moisture as much as sugar, and won't get sticky as fast.

Check out Sugar Delites, she has the pre-cooked isomalt.  All you  have to do is melt it in the microwave.  I used it for a lens on a camera cake I made a couple of weeks ago, and it worked great.  

You're definitely getting it too hot if it turns yellow. Are you putting the pan in a pan of cold water when it gets to the right temperature as you cook it? You need to do that to cool it down fast so that it stops heating up, or the residual heat will take it past the temp that you want it to be and it could start getting darker.

I agree.. try isomalt if you want something really crystal clear! 

@MYOM-Dominic wrote his top tips for working with isomalt here: http://www.cakecentral.com/tutorial/30598/chef-dominic-palazzolos-isomalt-tips

He recommends using distilled water to prevent minerals turning the cooked sugar yellow.

Count me in the "use isomalt if you want it really clear" camp!  Isomalt will caramelize at a much higher temperature.