Currently, adding a pricing matrix depending on sizes and colors is not possible in QuickBooks Online. I know the importance of having this kind of feature. I'll make sure to tap this to our developer's team. This way, choosing different templates or adding colors and sizes in the inventory might be given a chance to be included in the next product updates.
In the meantime, you may consider the third-party app that integrates with QuickBooks Online.
You may want to consider visiting our QuickBooks Blog. From there, you can see the future developments and the latest news about QuickBooks and what our Product Care Team is working on.
Please know that the Community is always here to help you out to make you and your business easy and functional. Have great day!
Intuit has acquired an inventory management app recently. You may explore it.
If your assembly process needs more feature, you may integrate it with a manufacturing app.