I am originally from Adams County and went to school with lots of working class Chican@s and poor whites who speak with what I call the "Denver" accent. Each of the four counties surrounding Denver have--as far as I can tell--distinct accents. Dougco sounds the most like GenAmerican and is very proper ('cause they rich) and Jeffco is also pretty indistinguishable, but has more of a Midwest twang than Dougco. Arapahoe, Adams, and most of inner-city non AAVE or immigrant English sound more similar and have a distinct sound.
First off, nobody says Dinver... it's closer to Danver.
We have a weird half-Midwestern, half-California vowel shift. It isn't super thick but you can notice it if you listen close enough.
First, the a in cat is kind of like a Minnesotan accent, but less horrible (sorry Minnesota). Almost cyat.
Second the i in pin and e in pen are not distinguishable. No, nobody says betch. But, it is in between the two sounds. Milk is closer to melk.
Third, the e in bed has shifted to be closer to bad. They are still distinguishable, but can get mixed.
Fourth the u in words like dumb is almost an a sound like dawmb.
Finally, the most noticeable vowel shift is in the oo in pool or Coors. In Colorado--even in Jeffco--we really draw it out like oo-uhl. The poo-uhl. Get me a Coo-uhrs.
Other tips: don't say walking, say walkin'. Don't pronounce t in the middle of words or at the end. Matt is more like Ma' (the ' like in Arabic) and kitten is ke'en. The double-d sound in ladder or whadever is almost like the sound r in spanish, a quick tapped r on the teeth.