Depends on the version of Access, but for 2002 and later, yes: use
Format... Conditional Formatting. You can color a textbox (or a whole
row of textboxes or other controls) based on values within the record
or on calculated expressions.
If you want to color (or bold or underline) a single word or words in
the text in a field, no can do, unless you obtain a third-party "Rich
Text Format" control.