*On how to solve lineart coloring... If you mean coloring the lines, you can always select 'Preserve opacity' and then fill with the original color... It'll be kind of a reestart...
If you are coloring the lineart in the same layer, I think you could try selecting the lines manually if they are thick enough and invert the selection, then delete, although it might not be very clean... If the contrast is big enough between color and lineart, you could also raise the contrast until the coloring is quite enough, then use the 'Luminance -> Transparency' option and repeat as many times as necessary...
If you have problems with the coloring itself, I guess all I can do is advice you to select everything outside the lines, invert your selection and fill with a base color for faster coloring...
I hope any of those was of any usage... If you want further advice, you can PM with a screenshot, maybe?
About the undo limit... Well, to be fair, even Photoshop has an undo limit, although it's so big it's hard to notice...! It's a matter of memory, if there was no limit, the programs could easily crash by exceeding the memory. Now, many programs have an option to change this limit, mostly Adobe ones, but I did as well made some searches about this subject and I really could not even find hints of such option existing... Again, it doesn't surprise me considering SAI is such a 'pocket Photoshop'
Sony-Shock
I've never heard of SAI having options for the undo limit... And I might be wrong, but I fear I don't see it being a thing!
On my long experience with SAI, I've come to realise is basically the lighter but much more limited little brother of Photoshop. Considering the incredibly limited memory the program has, I bet if there was a way to remove or increase the undo limit, it'd mess up its already fragile system...
If you tell me about the artwork, maybe I can help you, though! I've faced some ugly stuff before...
TheDeathMeister
Well... I'm just coloring my lineart like an idiot ( Should've used Adobe for coloring ) and i didn't found the outcome very appealing so I try to undo it. unknowingly I exceeded the undo limit and I forgot that some of the layers were still merged so... yeah...
I kindly want to know if there's a way to remove the undo limit on Sai
since I can't find anything on the Sai Interface nor the internet to help me find a solution to a very simple problem on why the hell is there a limit on a undo button.