Runner doubled up question

Question
We are in a co-ed, recreational, slow-pitch league in Iraq, playing with ASA rules (with a few minor "house rules" to adapt to our field conditions).  I made a call last night that was hotly contested by the offensive team. Although I'm 99% convinced that I was right, I've never come across this situation and would like a second opinion.

There is a runner on first. Batter hits a sharp liner to the firstbaseman, catching it for the out.  The runner on first had taken off, and is now scambling to get back.  The firstbaseman beats him to the bag, and I call the runner out.

The contested part comes from the fact that we have the "red safety bag" at first, that sits attached to the main, white bag, but on the outside of the foul line.  The firstbaseman stepped on this red bag and not the white bag, which is why the offensive team believed the runner to be safe.

My initial call was safe, because I believed that the firstbaseman had overstepped the bag (we play in about an inch of talcum-fine dust, making the ground hard to see); however, I immediately reversed my call to out less than a second later when I realized that he had actually stepped on the red bag.

Since the red bag is there for "safety", and the runner was sliding back into first, the firstbaseman (intentionally or not) avoided possibly stepping on the runners fingers by stepping on the other bag.  This is how I rationalized my decision to leave my call as "out" (in the face of a very mad offensive coach, telling me that the red bag could not be used).

Can you clarify how this "safety bag" works, please?

Answer
Hi Jim,

If you're military my only son is Marine Sgt. Ben Ambrose, God bless you all and come home safely.

Regarding the much less important double base.  It is only used when a play at 1st is being made on the batter-runner and then there are exceptions when one can use either base.  

Once a runner is on 1st it basically becomes one huge base.  This is a "live ball appeal" of a base left too early and the fielder may use either base.

Your call was correct.

take care

mark