Is there a way for me to view my work or my whole iMac screen in grayscale?
Yes you can! 

Follow these steps:


Go to Apple > System Preferences > Accessibility
In the left hand pane make sure Display is selected
On the right hand side you’ll see a number of checkboxes and sliders
Tick the Use grayscale checkbox


Your iMac’s display should immediately switch to grayscale mode.

TIP: Since you only need grayscale while you’re working on this job, you can tick the Show Accessibility status in menu bar checkbox at bottom left of the Accessibility preferences. This way you can access this setting as you need directly from the menu bar.