What do the email and phone icon colors mean?

On the activity timeline, you will see colored email icons like these...

The green-colored email icons are for emails that were sent from FrontSpin. The navy-colored email icons are from inbound replies to those emails. 

If you see brighter blue-colored email icons, those were from emails sent outside of FrontSpin...

When a user's email account is connected under SETTINGS => EMAIL SETTINGS => ACCOUNTS, FrontSpin monitors the user's INBOX and SENT folders, so if it sees emails that should be logged to the leads/contacts in FrontSpin, it auto-logs those for the user and they will have the brighter blue-colored email icon.

For phone calls, the green-colored phone icon is for calls placed in FrontSpin. The navy-colored phone icons are from inbound calls received in FrontSpin.