Art Advice Needed

My colleagues and I have been pondering ways to make the school more beautiful.  One suggestion was to paint the ceiling tiles in the school.  (You know, those ugly white ceiling tiles that can be easily taken down).  Well, I thought it was a wonderful idea, but now I am pondering the logistics.  I need some advice.  First, Has anyone done this in their school?  Second, If we did do this, What kind of paint should I use?.  Third, Will this break fire codes, and will the fire marshall make us take it down?  I would love to hear some ideas on this.

Washable tempera

I have gone most of this year with very few art supplies.  There were numerous problems, but basically the art order I had made this year got mixed up and I ended up either getting the wrong supplies, or not getting what I ordered at all.  After calling the company, I found out that it wasn't their fault, it was a mixup in the county's ordering system.  Anyway, to make a long story short, I ran out of drawing paper half way through the year, and am running extremely low on paints, glue, and pastels.  This means I have been begging for art supplies from everyone.  I have asked classroom teachers to send me any art supplies they are not using.  As a result, I have been given an interesting assortment of supplies.

One of the things that was generously donated was several gallons of washable tempera paint. Until recently, I had not used washable tempera in my art class.  I have always used Sax Versa Temp for my classroom.  I had not realized how spoiled I was.  Washable tempera is nothing like Versa Temp.  It is watered down, and sometimes dries transparent.  Students have to paint 2-3 coats to make their painting look nice.  I have been racking my brain for ways to make the washable tempera better.  Does any know of an additive that can be added to tempera paint to make it thicker?  I know that their are many acrylic mediums out there to change the consistency of acrylic paint, but I have never seen anything for tempera.  I would love to hear any suggestions.