Add standard colors shortcuts

I would find it cool to be able to pass colors as strings to some functions. Could we add an `enum` with a bunch of "standard" colors?

```ts
export enum Colors {
  red = [255,0,0],
  green = [0,255,0],
  blue = [0,0,255],
  ...
}
```

The issue however is to handle the bit depth of the image, and wether there is an alpha, which I don't know how to do in a smart way.