Hey there, @mammallamas!
Ryder here, from the Social Care Team at Shopify. Thanks for posting! Taxes can definitely be confusing at first, but I'd be happy to shed some light on how collection works in the United States!
Regardless of whether your store's location is in an origin or destination state, no tax will be charged on any orders to locations outside of where you have nexus. It sounds like the only physical presence/location you currently have for your business is in Indiana, is that right? If so, your Colorado and Washington orders shouldn't be charging tax, as they're outside of the state where your business is located. Because Indiana is a Destination state, any orders that come in from an Indiana shipping address will be taxed based on the zip code of the shipping address, determining state, county, and city taxes.
If you do have nexus in other states, such as Colorado or Washington state, you'll want to ensure that you setup taxes for your nexus as well. You can also learn more about United States taxes in our US taxes guide. If you still have any concerns, we always recommend speaking with a tax expert in your local region.
I hope this helps! Please let me know if there's anything I can clarify.