Doing a special pattern on adobe illustrator

I am facing a technical problem, and I hope you could help me !

 

My purpose is to make (as more automatically as possible) a dots pattern, which begin with red dots and finish with yellow dots for example, but not with a classical gradient which could add some colours like orange between the both. I just want less and less red dots, and more and more yellow dots. And by the way a composition in two colours only.

 

I tried with the pattern panel but did not find the answer. Could you have any idea how to make this, not manually ?

 

In attachment, you'll find a picture for example. The gradient is not perfect because manually done and on a small number of dots, but there is the idea.

 

Thanks a lot for your help !