I have seen so much dated and downright ugly accent tiles in my design career, that when I choose them for my clients, I prefer to select neutral finishes and repeat them. Keep this in mind when you read this post. If you are madly in love with the accent tile you have just installed or are about to, then read no further.
The following opinions are completely biased based on the above statement. . .
The hot look in tile is still mosaics, but if you are going to use them, go big or go home.
Like in this bathroom (above) or in this kitchen (below). What works about the backsplash here, is that it's the most important feature next to the Caesar Stone Countertop. This way it becomes the background instead of competing for attention with the limestone mosaic backsplash.
The backsplash tile in this bathroom [below] is colourful and fun, but what if you moved in and did not like orange? It's pretty hard to ignore the tile here as it's definitely the focal point. Better to have picked a more neutral tile and still painted the bathroom orange which can then be easily changed on a whim.
By the way, this brings me to another tip; with newly installed tile or granite, I like to pick a colour that coordinates with it, then it looks like you actually love your new finishes. To pick a colour that doesn't relate at all [to your finishes] starts to look like you have just moved in and have decided to ignore them with your colour choices.
The accent tile in this kitchen [below] at least makes some attempt to coordinate with the granite but I would have left it clean using just the subway tiles. I always tell my clients that it's the colour and accessories that pull a space together. Unless you are someone who plans on replacing your tiles every 5 years, it's better to keep them neutral as they are so expensive and messy to replace.
This tile [below] in your bathroom or kitchen [for example] pretty much dictates the colour scheme. Here your choices would be limited to some version of gold, yellow beige or [ouch] the green.
If you are going to get this artsy and creative [below] with your backsplash tile, then at least make sure it's the most important element in the kitchen. In this kitchen, combined with the busy granite, it's hard to know what we should be looking at. Busy granite and a busy backsplash does not equal beautiful, it just screams 'we-should-have-consulted-with-a-designer'.