Did you crush your seeds first?
The medicine in milk thistle is not water soluble, so you will get a stronger extraction with a higher alcohol content like 151 or Everclear. Generally, 100 proof is perfect for most extractions though.

100 proof vodka is a high enough alcohol content for milk thistle. Many plant constituents of milk thistle seed are soluble in water, but the silymarin itself is 'poorly soluble' (but soluble enough that people have benefits from milk thistle seed tea).

As you know (now), it's preferable to start with the whole seed/herb, soak it in the alcohol for a few days and then macerate it in a blender (rather than starting with powdered herbs that may have lost essential oils during the grinding/powdering process). But still, you seem to have done everything correctly, and the tincture should be strongly therapeutic.

Color? That's actually a tough one to use as a yardstick for therapeutic quality. Sometimes, sometimes not.

For example - what stage of the seed is best for harvesting milk thistle? In it's younger, milkier stage, or when the plant is totally dry/dead in the late fall? (typically seeds are best harvested after they're fully formed). The color of a tincture made from either would vary quite a bit (and of course, if herbs are overheated in the grinding processes that could certainly make them darker). The amount of nutrients in the soil (and varying soil factors) could play a part in coloration, as could whether or not the seeds were dried in the shade or sun.

This is why I prefer taste & smell over color as a 'qualifier for quality'. Herb Pharm's may be darker...but WHY is it darker? We don't really know.

If you compare (or have compared) the taste and the smell and still consider yours to be weaker (remembering that taste/smell can be affected by the grinding process), then in order to make it stronger you would open the jar and let some of the alcohol evaporate away. I wish there was some way to know 'how much' to evaporate.

Honestly, with what you've described (a very solid & thorough tincturing process), I wouldn't allow more than 1/4th of it to evaporate, or you may end up with something so strong as to cause an unpleasant reaction. A reaction wouldn't like actually 'cause harm', but hey...who wants 'em?

Heal ON!

Uny