Go to View > Master > Slide Master. Select the Text tool and click once on
the slide. You'll see a small text box with the cursor in it. Go to Format
Font and set it to Arial, the size you want, and the color of blue you
want, plus any other settings. Also check the box next to "Default for new
objects". That will care of any new text boxes that you add to a slide.
Now, still in Slide Master view, click inside each of the placeholders that
say "Click to edit Master title style" and Click to edit Master text
styles", and make similar font changes using the Format > Font dialog.
Finally, while still in Slide Master view go to File > Save as and select
Design Template(*.pot) as the type of file (when you select that, the path
in the dialog will change to point to where PowerPoint stores templates).
Give it a name that has meaning to you and press Save.
Now, return to View > Normal and continue creating your presentation with
blue text.