What is the cleanest way to do the following transformation in Pandas (Python) :

```
number   color
 10      blue
 15      red
 25      green
 35      blue
 15      pink
 30      green
  5      red
 20      blue
 50      red

```

into 

```
number   color
 10      blue
 15      FALSE
 25      FALSE
 35      blue
 15      FALSE
 30      green
  5      FALSE
 20      blue
 50      red

```

Essentially, I'd like to change all colors whose number is < 30 but that rule only applies if the color IS NOT blue.

Thanks !