@ Dave. Yes, in theory a flag in the table would do the trick. The problem is, that I've been asked to make two different systems, one that keeps detailed track of parts used etc. and another, where the information is just typed into a string. But I'll try to rethink the design with that in mind.
I would do this by having a memo notes field in the work order.
you end up with this
workorder table (include a Work Notes field)
workorder parts used table
enter some work notes on each job.
if need be, have a subform to select linked parts.
the job could just be a service, with no parts
if you need to replace a tyre, and brake parts etc, you can add the parts used.
You want to try to design the system to deal with all eventualities in a single streamlined system, It will be much easier than having multiple systems.
The colour is a red herring (sorry). You can either have a lookup table, or just free text. It only matters if you want to do a breakdown of bikes by colour - in which case you need a look up table, as otherwise you will get entry discrepancies and misspellings such as "red, red, read, pink, dark red, red multi" etc. If you have a lookup table, of course, you limit the colours to specific values.