No, your Laos visa does not need to be in color. Your Laos visa can be printed in black and white as long as it is readable, especially the QR Code. However, it is advised that you print your visa in color so that immigration officers may easily check it.
Here are the requirements for the printout of your Laos eVisa:
The PDF on an electronic device or a snapshot of the e-Visa are not allowed. Entry may be refused to those who cannot show a paper copy of the approval letter.