Actually, that would be a good way of testing whether Truprint's colour management was up to scratch. It is possible, in photoshop, to throw away all colour information and work in "black and white" irrespective of how the photograph you're working on looks on screen; if that is what you want.
Black and white (Monochrome) is notoriously difficult to print accurately as colour printers use coloured inks to print everything - colour and monochrome. Black is produced by printing the full intensity of red, green and blue, white is produced by not printing anything (it's the colour of the paper) and grey is produced by printing equal amounts of red, green and blue. A full range of greys is produced by printing varying levels of equal amounts of the three colours.
Unfortunately, its difficult to ensure that everything is working properly. The inks might not be true red, green or blue. The printer might not quite print the three colours equally and different papers respond to the colours differently. The result, therefore, is usually a colour cast and this will be more noticeable on a monochrome print than a colour one. Serious photographers working in black and white substitute the colour cartridges in their printers with ones containing only black and grey inks.
The other option you might think of is printing using only the black cartridge - as you would when printing a letter. This would work but you would simply get black and white with no intermediate grey tones - think "photocopy" rather than "photograph".
The solution is down to calibration, as I said previously. For complete colour accuracy your computer monitor needs to be calibrated to produce colours in a consistent and standard way and the device on which prints are to be made needs to be calibrated to reproduce the colours on a standard monitor with the inks and paper being used.
