The cost to paint an average size room (10X12) ranges from $380-$790, not including ceilings, trim or cost of the paint. DIY, this can cost between $200-$300. When estimating the cost, painters will start with how much paint will be required to complete the job. To know this, they first need to know the size of the area to be covered. The easiest way to calculate the size of the paintable area is to add together the length of the wall and multiply it by the width of the room from floor to ceiling. The resulting amount is the room's square footage. This total is a starting point, as it is not all paintable surface. The painters won't paint the windows and doors, for example, and they must account for ceiling trim and baseboards as well. The next step is to subtract the area of the doors and windows -- along with the square footage of the trim and baseboards -- to get an average. Then, use the same calculation (length x width) on the windows, doors, trim and baseboards, and subtract all of those numbers. The result of this equation is the square footage of the room's walls. This is your surface area number. (Painters will typically add a little square footage back in to this amount to account for extra paint, which may be required.)
I do not mean to come off with an edge, however, this is an article for people hiring low bid, uninsured, one man band painters out to "hustle" a buck. Hire reputable, established companies or hire someone you know or have a strong referral from. If you are arguing over watered down paint, ticky, tacky deposits, buying your own supplies, you have hired the wrong guy.
This article is outdated. Deep based colors were an increase in price back in the 90's. Most stores have a standard price for all colors now. The problems the author are citing are outdated and rarely happen. This is the 2nd time I've seen this article being emailed out, it's irresponsible of angies list to keep sending out this poorly written and inaccurate article.
The Lead Renovation, Repair and Painting (RRP) Rule establishes requirements for firms and individuals performing renovations, and affects contractors, property managers, and others who disturb painted surfaces.  It applies to work in houses, apartments, and child-occupied facilities (such as schools and day-care centers) built before 1978.  It includes pre-renovation education requirements as well as training, firm certification, and work practice requirements. 

Painting Contractor