I've never read anything containing an actual description of what the webway looks like once you are inside it. Any help?

(I'll love someone forever if they can point me to an actual picture.)

The book by Ian Watson the Inquisition wars had a lot of description....hold on Il see If I can find some extracts....

"ENTERING THE ELDAR webway was like walking into a tunnel of ice......At most
they might sense a fleeting ghost passing by, out of phase with themselves. Such was the nature of the webway. Each traveller or
group of travellers occupied a unique quantum of time. Two groups who set out at separate times from separate places could not
coincide at the same time and the same place within this galaxy-spanning network.

Whilst in the webway, one's sense of duration evaporated. Had one set out through the network just a few minutes previously? Or
an hour earlier? Or a day earlier? Impossible to say! In the webway even chronometers were completely unreliable, while one
watched recording a lapse of several hours, and then only of a few minutes.
It was this timelessness which would sustain the four of them until they could reach a gap in the rune-route, and emerge upon a
world. Tramping the webway was akin to travelling in a dream....

THEY STEPPED OUT of the misty blue tunnel into a damp and airy cave, green with ferns...

THEY HAD EMERGED, sprawling, into misty blue webway. The end of the tunnel was liquid, held back by some membrane which permitted the passage of living beings but not of inanimate matter. Was this membrane a creation of the eldar during an earlier
era? Or was it a phenomenon of the webway itself?"

So then… a Misty Blue Freezing Tunnel then, where you lose your sense of time because you occupy one slot of it AND you can vaguely sense the presence of others travelling in the same tunnel at different times forward OR backwards. The entrances are like liquid membranes that
permitted the passage of living beings but not of inanimate matter.

However bear in mind that this is the earliest early '90 40k fluff which includes among other things squats, sensei and IIluminati, so its not 100% canon (GW new fluff preface for the book claims that its the mad lies of a crackpot inquisitor) Check with Millardson an other Greybeards and assorted heretics on these boards. To date though there are very few specific eldar novels that describe it. Or at least that I know of.

As a recall, the Warhammer 40K comic Daemonifuge depicted the Webway as a shapeless expanse. Being within the Webway was like being surrounded by clouds on all sides. As you approached your destination the clouds would part revealing open space, Eldar structures, or whatever else was on the other side of the gate.

Actually there are several visuals provided in the Horus Heresy: Collected Visions book where you see the webway in the background as battles rage. It's depicted in hues of gold, red and green with swirling, neon,lace-like designs interlocking together in traditional Eldar fashion. Behind this layer is a red organic-like layer. The image gives the feeling that the webway is constantly shimmering and shifting with color and has an omnidirectional light source. There are also images of Eldar city structures silouetted in the foreground where cities may have been built within and abandoned.

I just imagined it was like being in a warp protected tunnel, like a shark encounter at Sea World. Chaos colored swirling gasses all around, maybe entities bumping against it. Pretty spooky I would think. Or maybe it is just an enter/exit sort of thing which does not last but a second. Those wacky Eldar and their tech!

The short answer is:

However the author wants it to look!

It has been depicted in different way by different authors. And according to GM rules on canon they may ALL be correct.

Such are the ways of the warp.

Thanks for the answers, everyone. Y'all have been most helpful.