Can I color orders from a specific form in the journey calendar?

Yes this is possible by means of a hidden free ride field, read more about creating and editing ride fields via https://taxiid.zendesk.com/hc/nl/articles/208414515-Free-ride fields

Take the following steps
1. Create a free ride field of the hidden type, make it visible to the customer with a name that is understandable. Consider, for example, "Airport booking"

2. Enter a default value, for example "yes" or some other description

3. Select the color marker that the ride may have

4. Link the free ride field to the form via, product settings / website order form / options free ride fields / select optional.

After booking you will now see a color marking on the order form.