Hi C., I'm a school counselor (formerly in k-6, now in 7-8).
IMO, 3rd grade is too old for color cards or color system. But I think it's the cut-off age (btw in 2nd and 3rd) so you could still use it.
Also, seems like you have 3 different things going on here- the color system, the raffle, and the token economy. I would narrow it down or you will make yourself crazy.
Token economy is highly structured and works great with kids who need that (SpEd, Emotional Disability, etc). It is a good tool for keeping serious behaviors in check. Since you probably have a Gen Ed classroom, you won't be focused so much on controlling or modifying their behavior as you are on just plain teaching them. I think you will get tired fast of running weekly auctions (and pricing items appropriately!) It will take a lot of work throughout the day to hand out money and then find time for an sale every few weeks... so I would consider running with one of your other ideas. Unless you are entering a "tough" school where kids are known for bad behavior or disrespect. Since you said private I am guessing that is not the case.
The color system- can work well, and it should just melt into the background of your classroom culture. I agree to adding one extra color above green. Here is an idea for you I have seen working well in 2nd grade: You have a big long strip on the wall with sections- Purple at top, green, than yellow and at the bottom red. Each kid has a clothespin with their name written on it. All kids start with their name clipped at green each morning. When they misbehave, they are asked to go move their clip down to yellow (the warning zone, or however you want to do it) From there it takes a positive behavior (or at least an obvious correction of the previous neg behavior) to move them back up. Of course if it gets worse, it goes to red, which is phone call home or discipline referral or whatever you decide to make it. The thing I liked about this is the small sense of personal responsibility for their actions that it instilled when they had to go move the clip down themself. And of course, kids would be so proud to go move their clip up to purple if they did something stellar that day. Save the purple for really "above and beyond" stuff, and maybe that means double tickets into the raffle that day.
I have also seen something in 1st grade, more simple, where the teacher had a big cloud with a lightening bolt coming out of it on her whiteboard. Throughout the day, if the kids did something wonderful, they got their name put in the clouds as a "brainiac". A misbehavior sent them into the lightening bolt. Can't remember the exact logistics but it was simple and cute. Probably 3rd grade is too old for that.
I like the idea about the weekly raffle. That should be pretty easy to incorporate into whatever daily system you have. The only issues- it's hard because a kids name may come out on a Friday that they happen to have spent the whole day in yellow zone or whatever... or a kid who had a total turnaround halfway through the year may never get the raffle because they just didn't get enough tickets banked in there compared to everyone else... Honestly, I used to run a weekly raffle and I would rig it. Strange as it sounds, the results being left up to chance just allowed for too many repeats and not enough chances for many "middle of the road" kids. Just something to think about.
Good luck, it is an exciting time of year! Whatever you decide to do just STICK TO IT, (maybe modify slightly if it truly is bombing), but if you switch systems, kids will never know what to expect and will never invest in any of it.
Have a great year!
S.