Thomas Jefferson 1857 5 Cents, What Color

Just want to know what color this stamp is, and why is the perf. trimmed like this.

This color is usually described as "red-brown." The perf is trimmed that way, because someone once took scissors to it and cut it for some reason; there's no real "why."

I know that there are also a Indian red, but it is not easy to see what color it is.
Red braun or Indian red.

The 1857 series was the first set of US stamps that were perforated. After 10 years of separating imperf stamps with scissors, people continued some habits even after the stamps were perforated for easy separation.

There are multiple colors and shades on the 5c, such as brick red, indian red, red brown, and brown. It is difficult to determine from a computer monitor. You can try looking at the Siegel Power Search for Scott 28 and 28A to try and see some comparison. With two stamps in-hand to compare next to each other it is much easier to determine.

In my opinion...
Using colors via images is the least likely method for determining a stamp identification. In fact, using stamp colors to ID a stamp in hand is typically very challenging and best left to people with significant experience and reference collections.

I do not have faith in any digital imaging unless the source has gone to great lengths in describing how they generated the image. Whether intentional or unintentional, digital images cannot be trusted.

Using Seigel, certainly a reputable organization, images should not be used in my opinion. Here is why, all the same stamp from Siegel images...


Don

Yikes, that is bad. I've generally been pleased with the quality of color representation in the Siegel printed catalogs that I have seen from the 1990s-2000's and use some of them for reference. When looking at photos of numerous examples side-by-side I can get a feeling for what are the key aspects of the colors to look for. With individual photos of scans online, it is much harder.

I have a feeling that as you go back in time in Power Search the images are scanned in from print catalogs.

Three stamps from a block of four currently offered on SG's website.

You had me at block of four

Nice block and the stamps look to be of the same colour. The three I posted should do so, but there are variations even when they are from a single block and scanned around the same time by Stanley Gibbbons.