Hello to all! This is my first post here. I hope it will be of help.
If you think a little bit more it is not so difficult. I assume that the time zone is implemented at phone level, so the phones in Texas and Colorado can show both the right time. On the system level however there is only one time zone - you have to figure out which one is the main. To configure Ring Plans as it was stated above you have just to add (or subtract) one hour. Let´s assume that the system is working with Texas time zone. So to configure RP (ring plan) for CO you just have to put working hours 6:00-13:00 workdays and 15:00-17:00 on Sundays (instead of 7-14 and 16-18). So the final configuration could be like this:
.......RP1................RP2.................RP3..............RP4
Su..00:00-23:59....15:00 - 17:00
Mo.00.00-23:59.....06:00 - 06:59....07:00-12:59.....13:00-19:00
Tu..00.00-23:59.....06:00 - 06:59....07:00-12:59.....13:00-19:00
We.00.00-23:59.....06:00 - 06:59....07:00-12:59.....13:00-19:00
Th..00.00-23:59.....06:00 - 06:59....07:00-12:59.....13:00-19:00
Fr...00.00-23:59.....06:00 - 06:59....07:00-12:59.....13:00-19:00
Sa..00.00-23:59.........................07:00-12:59.....13:00-19:00

RP1 - TX and CO closed
RP2 - TX closed, CO open
RP3 - TX and CO open
RP4 - TX open, CO closed