Telling which class w-space system you are about to enter appears to remain an art, or perhaps some kind of witchcraft. To the untrained capsuleer the indecipherable letter and numbers that float near the wormhole mean nothing, and coming at it from the wrong side only gives you the standard K162 designation that gives no information about the system beyond. It is possible to interrogate a database of static wormhole designations in order to determine the class of w-space you're about to enter, but it would be much more useful to be able to tell at a glance. But trying to inform the inexperienced pilot about the colours that bleed through somehow only leads to more confusion. Let's see if I can make visual identification easier.
First, wormholes are not simply holes in space, they are more akin to tunnels. The colours that surround a wormhole reflect not only the system on the other side but also that of the system you're currently in. The outer edge of the wormhole represents local space being funnelled through the portal before it transitions entirely in to the view of the system beyond. This is important to realise, as the different colours around the edge of the wormhole can potentially taint your impression of the whole. The example images I give in the body of this post are as representative of the main colours as I can manage, although I also include a more comprehensive matrix to aid with identification and visualisation.
It must also be noted that the colour of a wormhole only provides information about w-space systems. There are plenty of wormholes that lead to high-, low-, or null-sec space, and the colour of the wormhole will reflect that of the colour of the system on the other end of the connection. As the full range of system hues exists in each security level of k-space the only way to know the level of security on the other side of the wormhole, without jumping through, is to open up the information panel for the wormhole. The panel will inform you of either the security class of the k-space system, or that the wormhole leads to w-space.
The information panel also describes several tiers of w-space: unknown, dangerous unknown, and deadly unknown. These tiers split across the classes as follows. Class 1 to 3 systems are unknown w-space, class 4 and 5 systems are dangerous w-space, and class 6 systems are deadly w-space. Identifying class 6 w-space systems is therefore pretty straightforward. And if being the only w-space systems classed as 'deadly' weren't enough the lava red colours of the wormhole are also quite striking. There is no mistaking the fiery entrance leading in to class 6 w-space.
Moving down to merely 'dangerous' systems, the class 5 wormhole can be recognised by its prevalence of black, slightly tinged with orange.
Wormholes leading to also dangerous class 4 w-space are orangey-green, and quite distinctive if only because I do not believe there are k-space systems that generate such vivid wormhole colours.
The wormholes leading to the highest level of plain and far from dangerous 'unknown' space are also quite distinct, being essentially a light grey. These class 3 systems are about as bland as the wormhole colour, and you barely need to check your directional scanner when mining in one, this information in no way tainted by the author's current hunting grounds.
Most confusion comes from the difference between wormholes leading to class 2 systems and wormholes leading to class 1 systems. I'm not sure what the fuss is all about, though.
Blue-green on a black background, it's quite clear. Just like the wormhole leading to class 1 w-space.
And by 'just like' I really do mean 'just like'. Blue-green on a black background. But if you look carefully at the wormhole leading to class 1 systems you can see a small cowlick of green at the top in the centre, like Superman's barnet. It's a subtle distinction between the two types of wormhole, but a trained eye can discern the difference. To add to the confusion, wormholes leading to class 1 and 2 w-space are those most often confused with wormholes leading to k-space. It's always best to open the information panel to check these.
Now let's look at how the originating system affects the colour of the wormhole. I have collected a range of images from many types of wormholes to illustrate the differences. The matrix format should make both the originating and destination system colours clear. The rows show the originating system and the appropriate colours are reflected around the edge of the wormhole. The columns show the destination system and the appropriate colours are reflected in the centre of the wormhole.
Although there are gaps I aim to update the table as I encounter the missing types. Larger images lurk behind each wormhole.
Hopefully with this information you will be able to tell quickly and easily the class of w-space you are about to enter. Being able to do so at a glance removes the need to jump in to the system to find out, particularly if you are looking at the K162 side of the wormhole.