As you have been told, "digitals" are replacing the BDU.
To answer your question, when the BDU was developed back in the 80s there were three (origially four) kids of BDU. Desert, Woodland, Arctic, and "Urban". Urban was a grey, black and white mix designed for fighting in cities. (If the Soviets had come into West Germany there would have been a LOT of street to street fighting, Germany is very urbanized.) I don't think that the "Urban" pattern was ever officially issued, but it was very cool to wear it in the late 80s. I think some SWAT teams adopted it. There were also some all black BDUs made, but those were only for the civilian market as far as I know.
Units were issued Desert, Arctic, or Woodland based on where they were going to be deployed. If you were going to be operating in a snowy enviormnet you got Arctic. I was never issued Arctic but I believe it was rare and most restricted to coats, etc.
Units that got sent to the CENTCOM Area of Operations (Iraq, Iran, Saudi, Qatar, Sudan, etc.) got desert cammo. Units that went to Korea, Germany, etc. got woodland. Since most units were NOT in Centcom at this time, woodland was much more common and thought of as the "standard"... at least till the current war started and people started getting more and more desert BDUs. If we had gone to war in Antartica I suppose the white arctic cammo would have been more common.
After the Gulf War One in Kuwait in 1991 the Desert Cammo pattern was redsigned. The original Desert Cammo was called "chocolate chip" because it had lots of little black dots as part of the pattern. I've seen Iraqi units wearing BDUs with this pattern on them.... I guess they were left over war stocks from 1990.
The USAF tried a blue camo pattern BDU as an experiment about 2003 but it was literally laughed out of service...EVERYONE thought it was an incredibly stupid idea... I heard it compared to the "power rangers" and people said the only thing the USAF blends into is the blue office upholstery.
In any case, all BDUs are getting phased out now in favor of the digital cammo uniforms.
That is probably why the Civil Air Patrol still has them... you are most likely getting the left over BDUs the Army can't wear anymore.