The one thing that I dont think has really been addressed for the OP is the volume of the pour.
The OP, Siduri, specifically referred to a 30ml pour. What she did not refer to was the style of the pour, i.e., whether it was ristretto, normale or lungo; or whether it was pulled through a single or double dose. She also did not refer to the size of the dose. All of this might have been important, but since Siduri doesn't own an espresso machine, not so much.
We (or at least I) didn't get into any of this with Foodnfoto, but it seemed like addressing the "dark roast/crema" association took precedence. I added some more stuff in the hopes of getting a dialogue started with her. She's intelligent, knowledgeable, charming, and a fun correspondent. I'm just selfish.
I would highly recomend having your porta filter modified to remove the entirety of the bottom portion. They call it a "naked portafilter". So basically it eliminates all metal contact post basket. The main advantage is that it will allow you to see the liquid as it is pressed through the coffee grinds.
Unless you have a few, it's usually a better idea to buy an OEM, naked pf (portafilter) than donating your only stock pf to the cause. There are times, lots of times, when you'd rather not go naked.
A properly fitted basket doesn't contact the bottom interior of the pf in any case. If it does, the basket won't seat properly. A naked pf will allow you to use a very deep, "triple" basket. The espresso itself touching the bottom of the pf as it funnels down the spout isn't a problem.
You overrate the utility of a naked pf. The primary benefit of a naked pf (portafilter) comes in revealing errors in distribution. Poor distribution causes channeling. Channeling results in multiple streams, rather than a single stream emanating from a cone (caused by surface tension), which is what you get with good distribution (assuming an appropriate grind for the basket). You're right about one thing, you can't really see and cure channeling without a naked pf.
You will see errors in your tamping and pre tamping filling of the basket, allowing you to adjust your technique over time.
What tamping errors are you talking about? In my experience, a naked pf won't show much about tamping, unless your tamps are way off level or your tamper is way too small. You can see either of those errors by looking at the top of the basket after you've tamped. As long as you're level and reasonably consistent, specific tamp pressures aren't very important. Neither is polishing the top of the puck. Nor is "tapping" the pf. The importance of consistent tamping, is that it allows you to control the time of the pour with your grinder. The length of time it takes to pull a shot has a great deal to do with whether it's under, fully, or over extracted.
You can see the color change from the stream whether it comes from a naked pf, or a regular pf's spout. You can also see it in the cup on the surface of the pour. I think the last is the surer diagnostic, but we all have our ways.
It's important to realize that you have to spend a fair bit of money (or buy used and do your own refurbishing) on the machine/grinder combination before you get enough control and consistency over temp and grind to do a lot with using a naked pr to teach you better distribution. Most consumer espresso machines and grinders aren't there. That statement is limited to when a naked pf becomes useful. I'm not saying you need to spend thousands of dollars for decent coffee, to enjoy life, or enter heaven.
In my opinion, the palate and the Mark IV GI Naked Human Eyeball are more important tools; a watch with a second hand and a scale which can read to the nearest 0.1g are the most important mechanical devices; and after those, perhaps boiler and brew pressure gauges. A naked pf is nice, but it's somewhere down the list.
Also, as the pour progresses, you will see it change colour. Once it starts to turn quite light in colour, end the pour. It doesnt really matter what the volume of the pour is. If you aim for a certain amount of liquid, you may be adding a lot of bitter over brewed coffee to your cup.
You're talking about "blonding" Blonding is a sign of degree of over-extraction. Different styles of pours go further into the blonding process; ristretto less than normale, lungo more.
It's tricky to pull meaning from the volume of a pour, because so much depends on the amount of gas in the coffee, and that's highly variable. The weight of the pour in comparison to the weight of the dose is extremely useful, though. Dose/pour expressed as a percentage is called, "brew ratio." A traditional normale is about 50%, a modern is closer to 75%.
With both of my favorite espresso blends I dose at around 18g and pull at around 27g for a brew ratio of 67%. I don't always use a scale, instead using a timer on my grinder to dose, and using a watch and an eye on the blonding process to measure the pour. But when I do use a scale, I find the brew ratios to be very consistent.
Are you fellas mostly using small home roaster units? Anyone a bowl and heat gun roaster?
I'm currently using a HotTop Programmable 2 which suits me fine; before that I used a Behmor; and years and years ago, a Whirlypop. Never a bowl and heat gun, too demanding, too complicated. If I had to do over again, I'd probably get a Quest M3 for the extra control but would be just as well if not better off with the HT.