You know what I think, that was no coincidence. That rainbow was, I believe, a sign from your mom so please accept her gift with the love it was given.
We all grieve in our own ways and to our own timings. Maybe you are not the type who will have a melt down. Maybe that is something that will happen at a later date. Whatever comes will be as you need it to be for your own healing.
I am wishing him good luck in getting the dream job.
I am so happy for you. Hopefully one day we will all be able to think of our loved ones and just smile with the memories.