I deliberately made some links visible (changed color) in a recent post after some trial & error, but it's significant extra work.
Basically,
(1) select and copy the URL the link is to point to
(2) write the text you want to be visible as the link, and select it
(3) Click the "insert link" control.
(4) When it shows the dialog asking for the URL paste the URL you copied (I like to hit "Ctrl-V")
(5) The link will be posted. Look at the source pane, find and select the text in the link code.
(6) Click the "font color" control. Select a color to be distinctive from the normal black (I used dark green). The text within the link code will be enclosed by nested font-color code.
(7) when the post saved or previewed, the link text should show up in the color you selected.
("Should" of course is often a considerably different thing from "does", but I expect it would work for most everybody willing to take the trouble.)