Photoshop can be used to convert line-art sketches into color "paintings."  Here are three houses where I have done that.  Different techniques have been used with each house to give it interest and individuality.  

House #1 

House #1 with blue sky.  Usually painted architect sketches have an unpainted or white sky.   Here I have added a very pale blue sky.  I think it enhances rather than detracts from the image. 

House #2

House #3

house 3