flutter: prefer const for Color class - #197

I could merge this, but if you are thinking in adding to other things, it will be very hard. You will never be satisfied with const in Flutter. What do you think? Because lint will now complain BorderSide is not const.

I thought about addingconst to other classes, yup it's hard to estimate as well as impl because I need to add more logic that will check non const children, thus thinking where it would be more relevant and less error-prone.

Const will not bring any benefit to your code. I can merge this, but really don't worry. If your app has 2000 const or none, it could be 1% faster. I once added hundreds of const and had no difference in benchmarks.

Most likely the compiler will optimise, but due to some lint rules we follow at work this will stop those screams at least.

Yeah, but the issue is that everything else except const will still scream :( so this is just moving the lint error to somewhere else, but will definitely still happen. I think there is a dart fix that auto-fixes that now, so you will still need to run it, or disable the lint (I recommend disabling the lint)

In Flutter, the correct syntax is Colors.white without const. The Colors class in Flutter provides predefined color constants, and white is one of those constants.