If you're attempting to get a non-colorblind user's attention, yellow is actually the most attention grabbing color.
Yellow is less associated with anger and frustration (although it is still sometimes associated with those feelings), it is generally shown to be a more positive color.
Red does have more of an association with errors, and as @user12999 mentioned, things that are overdue (you can kind of lump this under the same category of 'error'). You'll find that yellow is more often associated with warnings than errors.
Today we have red notifications on iOS and Facebook, where users love to see them (at least on Facebook).
When considering Facebook and iOS's notification icons my mind goes immediately to colors that contrast well with red. Blue is one of red's triads and thus they contrast well -- therefore considering Facebook is mostly blue, red pops out the best. On iOS my opinion is that the badge was originally associated with the primarily green phone and text message icons and green is red's complement. As well, you'll find that the other original primary user of the notification badge was the mail app which is primarily blue.
In summary, if you're just trying to draw attention to an item, I think yellow is your best bet unless the item is overdue or an error then you should go with red. I would also urge to consider @Bevan's excellent point on not only grabbing attention by color, but by other methods of emphasis he has noted as well.