Removing the conjunction you get 3 sentences

We use actually to indicate a new topic of conversation

We use actually to indicate a change in what is being talked about

We use actually to indicate a contrast in what is being talked about

"Contrast in" is used in identifying the subject/criteria of contrast. For instance, "Contrast in appearance"

The other versions are generally used to actively compare different instances.

Removing the conjunction you get 3 sentences

We use actually to indicate a new topic of conversation

We use actually to indicate a change in what is being talked about

We use actually to indicate a contrast in what is being talked about

"Contrast in" is used in identifying where the contrast is. For instance, "Contrast in appearance"

The other versions are generally used to actively compare different instances.