What if your neighbor has painted your wall which faces her garden and you do not have access to it as there is a dividing fence It was a flat roof which was renovated into a pitched roof kitchen?

You need to check with the department that issues building permits in your area, since it all depends on the common property laws in your county/city.

Generally, if it is your wall on your property, defined by a single tax ID number, then you can control if it gets painted, what color etc. If the wall is a common wall, generally found in condominium projects (with a Homeowner's Association), etc. or if your property is governed by CC&Rs (Contracts, Covenants & Restrictions), you need to check the language of those documents.

If your wall is separate from all other property, then your neighbor does not have the legal right to paint the wall and you have the right to demand that they return the wall to the original color. This is fairly straightforward if your property is not governed by the aforementioned documents.

If you are governed by CC&Rs, HOA, etc. you need to check to see if your neighbor hasn't violated the terms of those agreements. Check to see if they can change the color of their outside facade, plant vegetation, etc. The next step is to check to see who controls the maintenance of common walls. Generally, a HOA participant can only change the interior of their property. This helps preserve property values, etc.

I would start there, and talk to an attorney once you have checked these sources if you have any further questions.