'shirt' should be an option as well as t-shirt. Unless you wanted to be very specific, or you grew up saying, would you say t-shirt. Most people I know just say 'shirt'.
But we have a report from the same time as your comment for "I do not want that yellow shirt." - which is "košile", not "triko/tričko". Although some people just say "shirt" instead of "t-shirt".