I’ve never had much luck getting final beer color to match what I want, so I’m wondering if it’s possible to do a grain ‘tea’ or something with a very very small percentage of a test grain bill. I’m thinking along the lines of 10 g crystal, 20 g pils, 5 g cara red, that sort of thing. Anybody tried this before? Does it scale?
Really? I have no problem with the color it’s the flavah that causes me heartache.
Try your proposed method with a French-press. 
What about steep time? equivalent to mash time or should it be OK with just a coffee’s worth of time?
I went through this during a pro-am brew session. We measured different quantities of grain and looked at what happened in 1/2 litre of water to make tea. We kept steep times to 15 minutes as we were trying to get colour, not extract.
We used a french press.
All of that said - sinamar is a wonderful thing if you need to adjust colour and won’t result in you watering down your beer. It’s just a bit expensive.
You can cold steep carafa and use that to add color, or cold steep the grains you mention, leaving out the pils malt. With the pils you have to do a mash, with standard steeping grains the temperature is much less important and since you’re just trying to add color I would skip mashing.
If you are trying to minimize roast flavors you can still use carafa, just grind it as usual, put it in a french press with some cold water, let it sit over night, boil it briefly, then add it to the beer.
If you are using the same grains as in the recipe, then I’d do a warm steep of 30 minutes or so, boil briefly, and add it to the beer. I haven’t done it, but I can’t think of a reason it won’t work.
I’d ask what is your method of determining SRM first. I’ve found it difficult to match the color to a beer unless you do it a very specific way. You can’t hold your glass up to the computer monitor and depending on what site your on, the color varies…you have to have ‘the card’ and a certain sized glass the beer goes in and hold it to the light properly… How far off is your SRM anyway?
It’s really more about trying to get a beer the color I want it to be, as opposed to true SRM, but SRM’s a handy way of saying what it is I’m going for.