If you mean white lettering out of a red solid (or tint):
Draw a rectangle to the size you want, fill it with the desired colour, draw a text box and type your text and format it. Select the text, and from the lettering fill, select white. (If the lettering doesn't appear, Object > Arrange > Bring to Front)
Make sure you check what color your text actually is. There is a big difference between “no color” and “white” (CMYK=0,0,0,0).
The Lego thick font is an inline font; changing the stroke/fill of the lettering will only affect it's border and not the area within. You'll need to convert the text to outlines and do some path manipulation to get the look you want. In the case that outlines and compound paths may be unfamiliar, here's a Dropbox link with the unaltered typeface and a couple of outlined and manipulated versions Dropbox - Lego.indd. Let me know if this helps.