*not sure if those hologram foils should be handled like regular stickers or not, currently treated as if the front side is printed chrome silver. Real ones seem to be available both with white and silver backsides.
*I don't have much experience with textures in LDraw, so hope everything is somewhat correct

See also:
https://forums.ldraw.org/thread-28514.html?highlight=holofoil

I think the fallback has to be a black surface with some random coloured spots.

Fixed the bug loading textures on the 3D viewer

Well, looks like both top surfaces are visible at the same time...

The first quad:
4 383 -22 -.25 9 -22 -.25 -9 22 -.25 -9 22 -.25 9
Duplicates the TEXMAP geometry and needs to be removed

The fallback quad should not be color 16.

*removed first quad
*changed fallback colour to 383 (Chrome Silver)

Should this line stay as is or be changed to colour 16? I couldn't find any details on this in the TEXMAP specification
0 !TEXMAP START PLANAR -22 0 9 22 0 9 -22 0 -9 169656a.png
0 !: 4 383 -22 -.25 9 -22 -.25 -9 22 -.25 -9 22 -.25 9

@Magnus:
Firstly, whilst the image may give the impression that this surface looks "black", it's really just the reflection in the photo. The actual part is very mirror-like (except that the dots break a clear reflection to a degree). This photo might give you an impression of the foil from various angles:
http://www.peeron.com/catalogs/1994/medium/18/?id=58

Secondly,
I don't think that hard coding the spots is the right way here.
My reasoning for this be that it's technically not a "pattern" by any way, but instead a "colour" we just can't replicate at the moment (think of it more like the rough surface of slopes or the marbled texture of old pearl metallic parts).

If I get the discussion here https://forums.ldraw.org/thread-24126.html?highlight=texture right, then Fallback geometry is not strictly required to match the pattern.

Similar patterns that are hard to reproduce as vector images (like https://library.ldraw.org/parts/1393) use a single colour quad as Fallback as well.

Whilst it might be argued, that this part has indeed the dots as "pattern", because it's otherwise plain, I think the overlaying goal should be a uniform approach of these foils. Most other foil stickers have a "real" pattern applied over the foil. Previously, the foil itself was ignored entirely and replaced by printed silver (colour 80, which I think is not the correct silver btw). This is kind of the idea I had in mind for the fallback, as it is the most close approach to a simplified version of these stickers. Compare https://library.ldraw.org/parts/1075, https://library.ldraw.org/parts/1076.

Lego'S instructions often use this approach as well: http://www.peeron.com/scans/6991-1/51

From certain angles, this foil does look like a plain shiny silver surface, from others you see the dots. So
my idea would be, that if TEXMAPs is available, you see the effect, if not you see the silver. If some renderer can actually replicate the hologram effect by some method, then the surface should probably be single colour as well to avoid issues I guess.

While I am not entirely sure about the right way, I think that ignoring the effect entirely is preferable (if TEXMAP should not be used) than to have a hard coded one (it also probably looks worse than plain silver).

"Should this line stay as is or be changed to colour 16? I couldn't find any details on this in the TEXMAP specification
0 !TEXMAP START PLANAR -22 0 9 22 0 9 -22 0 -9 169656a.png
0 !: 4 383 -22 -.25 9 -22 -.25 -9 22 -.25 -9 22 -.25 9 "

Yes. Make it 16.

*changed to 16

The whole point of having a fallback pattern is to give rendering SW that can not handle a texmap image, something visual to show instead of the texmap image.
A user looking at this part expect to see something, not just a "silver surface". They expect to see a "Glitter Space Panel".
How you choose the create that pattern is up to you. A blank surface is, IMHO not enough.

A detailed fallback isn't required but I'd recommend making the fallback quad Black. That said, I've used Rolf's img2dat in The past to create a rudimentary fallback.

I hope this time it won't break the server :S

Ok, I admit that this Sticker is a bit of a special case, since its unprinted (still not sure if adding a pattern where there is none is technically correct by LDraw standards). The instrucions for Set 6339 have a similar approach though.

*added a simple fallback pattern vaguely based on the Bricklink photo
*I did ignore the center vertices for the disc/ndis prims. Would it be necessary to remove the T-junc there?
*since opinions tend more towards black than silver, I went that route, but did at least choose Chrome Black to keep the shinyness. I am not sure if this makes the part too dark (Lego tends to use silver in most cases).
*the "random" colours were chosen from the available chrome colours for the same reason

Side note:
As far as I could find out, this particular type of foil was only used on 4 different sticker sheets (168275/6949, 168295/6959, 168285/6991, 169656/6339). Two of which have already been made into LDraw in the past.
There have been way more holographic foil stickers made, but none of the later ones used this stict grid pattern on the foil.