Re: isit possible to change colours of grass?

No, it is not possible to change the color of chlorophyll. Certain plants do 
have leaves that are light blue, blue-green, gray, purple, red, white, or 
yellow. Examples include coleus, caladium, croton, and blue Colorado spruce. 
Wyman (1986) has an extensive list of plants with nongreen foliage. Those colors 
are due to other pigments that dominate the green of the chlorophyll. Silvery or 
white leaves can also be the result of hairs. There is a blue fescue (Festuca 
ovina glauca) which is usually grown in clumps as an ornamental grass rather 
than as a lawngrass.

It is possible to paint lawns as done on football fields. 

With genetic engineering, it might be possible to create lawn grasses with 
nongreen leaves. 

Reference

Wyman, D. 1986. Wyman's Gardening Encyclopedia. New York: Macmillan.