[Paint brush won’t work on blank pixel layer?]

Found the answer myself,the protect Alpha is on.

[Paint brush won’t work on blank pixel layer?]

Hi, as I say  in the title, I am not able to paint on any blank area in a pixel layer with paint bush, but I can use other paint tool to do so. So to paint on a new pixel layer, I have to fill the layer with other color then start to use paint brush,if I erase an area the paint brush won’t work there. I discover this while trying to follow tutorial “changing eye colour ” but stuck at 6:53.nothing happens when I use the paint brush. Hope some one can explain this, thanks.

[Painted color is lighter than brush color]

Thanks every one for your kind reply, this problem disappears by it self, I am not able reproduce at this point, will keep a screen shot next time.

[Painted color is lighter than brush color]

Hi I am new to the Affinity, pardon me if my question seems silly. I am experimenting some basic stuffs right now, when I try to paint on an imported photo, the color goes on the photo will be lighter than it shows on the right side of  brush panel; if I start with a blank document then the color goes on is the same as it displayed on the brush panel; brush settings are identical, can somebody explain to me why? thanks!