Is there a place in Netsuite to add Item dimensions? What about other physical characteristics like Color, etc?

There are some out of the box fields like weight, but you can create custom fields and source those fields from custom lists, so you can have a field for any characteristic you can think of

We have a series of custom fields for L/W/H of the item as well as the packaged (shippable) box, both in metric and imperial. Document and name carefully if you go this route. Trust me.

agree with @Mark C, when you create your fields, make sure to put a detailed explanation in the help section. Takes a minute now, saves hours later.