I have 3 questions about exporting for iOS and Android app development.

I have a PSD file at the iPhone 6+ size of 1242 x 2208 pixels.

1. Can anyone tell me exactly what @x sizes I should use when exporting for:

(a) Android app development
(b) iOS app development

2. For icons which may be displayed in black or grey or a color, do you export and save them in their individual colours or just as black or white and let the iOS/Android developer apply the colour in code?

3. If an icon is filled 60% black would you export as 100% black and let the developer alter the fill in code or export it with 60% black fill?

Thanks for your help.