Purple (Barney's) is standard for $500, yellow or orange-ish (pumpkins) is standard for $1000 and brown is the most common color for $5k, although colors for denoms over $500 can vary from casino to casino. Cheques over $500 sometimes have a larger diameter, but this is more common for $5k and up.
I've never really been....shocked per se. When I was in Vegas back in April 2011, I sat next to a guy at a Pai Gow Poker table at Caesar's Palace. I was betting the $25 minimum per hand. He was betting $500s and $1000s like they were nothing. He was a nice guy to talk to.....we had some nice conversations during the time he was at the table (and showed off his chips a little bit....showing me what they looked like....the $500 chips (don't remember....think they were purple)....the yellow $1K chips....and a brown $5K chip). It was certainly an unusual (not in a bad way, though) feeling sitting next to someone gambling large sums of money while I'm just the el cheapo one betting the minimum.
Too bad he didn't throw you some extra playing money. It's been known to happen.
The first time I ever played at a $25 table was on my ** birthday at Harvey's South Tahoe. They used brass insert cheques at the time and the $500's were a bone pink. (All of their colors were weird. The brass insert and cheque color give away the year range for those who are interested enough to check.)
Anyway, I was playing with one other player who was dressed in a very expensive suit, tailored shirt, expensive cuff links, watch, etc., but who looked like he'd been in a wrestling match with his suit on, lost, and then spent 12 hours in a sauna, also with his suit on. (Interestingly, he wasn't drunk.) He was betting between $300-$500 a hand, two hands at a time and losing his ass, pulling thousands of dollars in hundreds out of pockets I didn't even know he had (money plays, mostly.) A short time after I sat down he started winning and soon had over $8,000-$10,000 in cheques in front of him. I had quietly won about $500 and announced that I was quitting, since I was usually a $2 or $5 bettor and had had my fling.
"You can't leave," he announced. "You're my good luck charm." I declined and he insisted. I finally offered to stay another 20 minutes for $500 and he tossed me a cheque without hesitation. I played out my time at $25 a hand, mostly even, and left. He got what he wanted and so did I. To him it was less than one bet, and he got his mascot and friendly company. To me it was a lot of money and it doubled my winnings that night.