The included HUD basically changes out the textures on the dress for 10 color variations of this sort of floral pattern. It is actually quite nice when you look up close. Good detail and there's a shadowing to the flowers that makes them look embroidered or woven-in vs. simply colored.
Want the dress in blue, teal or black? Just click the HUD and the magic happens.
Now for the fun part. Go onto the SL Marketplace and do a simple search for "Morgan Dress" without the quotes. You'll find maybe close to a hundred variations on BD Morgan. Some are sold as single colors, some have different textures for top & bottom, some have HUDs and some even add a fabric neckband. ALL FROM DIFFERENT CREATORS! And all at prices that are all over the block -- from $99L for a HUD-driven 5-color version to single colors for $149 to as much as $399L for yet another 10-color HUD version.
Above is one example of a single color from Black Rose for $99L. The creator has made their own sort of stripey texture and added some banding under the bodice and at the bottom hem.
So how does this happen oh mesh newbie? The answer is templates! And here's the grandmother of all these variations! The seller offers the dress in 5 standard sizes plus fitted sizes for the most popular mesh bodies including Maitreya, Slink, Belleza and TMP. That's a total of 12 meshes in all plus all the UV and Shadow maps and original DAE/OBJ files for popping into a 3D package all for $1300L. Not bad.
Now since the source files are full perms (you actually download them separately outside of SL), it's possible for content like this to get shared (aka ripped off). I have no idea if that's happening with Morgan but it's certainly possible.
The question you may ask though is why use a template? Why don't creators make their own from scratch? Well as a recovering designer myself, I can tell you it's really really really hard to do mesh. OMG. Unless you are super skilled at 3D work (using Blender or Maya or something), your learning curve to do something even as simple looking as Morgan is going to be really steep. It's not at all like making appliers for t-shirts. And then consider that there are 12 meshes for 12 size variations and riggings supplied with Morgan. That means you have to have Slink, Maitreya, TMP, Belleza and the FIVE standard size models in your 3D program to get them tweaked correctly.
So that's why you'll see many designers focusing their skills on texturing and adding value to something like Morgan rather than try to design them from scratch. Now some designers DO make their own meshes. Shoe-oriented companies (like my favorite KC Couture) mostly due their own meshes as do mesh body creators. But others, like another fave of mine, Inga Wind, do some really amazing textures on mesh templates. Often designers like Inga will create an outfit complete with shoes, accessories and jewelry to add value to what starts as a template mesh.
Now as to the HUDs to change colors/textures, those are fairly easy to come by. There are lots of full perms scripted HUDs on SLM that you can buy, load with your own textures (full perms) and target the mesh template. Since many mesh templates have "faces", the HUD can also target a specific part of the mesh to change say the shoestrings or buckles or bows or whatever might be available. Note that this discussion on templates doesn't just apply to fashion. It can be for almost anything rendered in SL including buildings, vehicles, plants, furniture, etc.
Is this sort of info worthwhile to you or is it too basic? Let me know!