I had such a feeling. That was why I asked. I understand how it is as all my skills were self taught so I had no idea of a better way to do some things. I am fortunate that recently I have met people who I can ask about these things.
Yes, there are much faster ways to apply base colour. The method I am using now has it's flaws but is far faster than using the brush tool. This might be allot of words and I am reallysorry about that but I really think it will help.
Simply go to the line art layer and select the area you wish to colour with the magic wand tool, in this case let's say the face. Then you hold shift and continue to select any other exposed skin in the drawing.
Once all the parts you wish to colour with the skin tone are selected. Usually just filling in or using the magic wand tool will leave an annoying 1pixle think line around your colour. go to the tab on the top control bar marked "Select" and under that find the "Modify" option. "Then you must enlarge selection" by 1 or 2 pixels depending on the size, so the selection falls just under the line.
Next make a new layer just under the line art layer wich will become the colour layer.
Then right click the selected area with a lasso or magic wand and select "Fill". You will get an options box. You need to indicate that you wish to fill the space with colour and then un-tick the box that says "keep layer transparency". Then it will fill the selection with whichever colour you have as your primary.
The main flaw with this method is that sometimes there are small specks that remain uncoloured. To fix this I keep a bright green fillscreen layer at the very back so the green shows up clearly through any gaps in the colour.
I have heard people use a method of colouring that involves vector masks but I have only just begun to use vectors so I do not know about this so if anyone knows a better way then please correct me.
A few other tips to keep your production time down: Keep all the layers for separate panels separate in different folders marked "Panel 1", "Panel 2" etc. Don't mix the layers between panels because then things get confusing. I would also recommend making custom colour swatches for all your characters so that when you come to colour a character the colours are just waiting for you in a tab rather than having to upload an older drawing and get the colours from that. And also not really anything to do with colouring but once you figure out the vector pen tool, so many more options become available for line art. I guarantee that with all of this, applying base colour to a whole page will take no more than an hour per page. I am really sorry for the wall of text but I definitely think it will help. Or if it was to long and you did not want to read my long winded explanations then that is okay, I'm sorry about that.
I am the MISSINGNO
Current world record holder for the longest case of the sniffles.