It was just for show.......even gut like Vctor Imperial had a blue spiral strand (Chris Evert used it through the 70s) and PDP had a gut with a green strand running thru it.
There was some with red and als orange.........as for the stings in the above sticks those more likely than not are made of cotton or twists of spun polyester (nylon 6,6) was very commonly used and wrapped by a plastic covering.
The interior stuff was simple nylon filaments that were twisted. They were wrapped with a nylon sheath which had color spirals. Once the sheath was compromised, the stuff started to shred like cotton since the nylon was not up to par with the monofilaments today. Strings were terrible and not durable, which was why NG was the string of choice.
String in that 1st racquet is just typical nylon strings used back then.
There were a number of variations of the nylons but most were similar, some were a little cheaper, like the one in that 1st picture.Being a cheap nylon, I wonder why someone would piece it together as even though the entire racquet is not in picture I count 6 knots.
A quality tournament nylon back in the day would cost a stringer approx. $1.00/ racquet if they had a dealership and purchased a reel. This string in 1st picture is way less in price.
I still have some strings from the wooden racquet era as I strung a lot of wooden racquets back in the day.It took about 33' to string a wooden, and nat gut was supplied in 2 -17' sections so they gave a little more than needed.
I started playing in the 70's. Those were your typical nylon strings back then. Blue Spiral was one of the names for those strings. They weren't great for performance, but they were durable. Back then you didn't have the choices you have now.
I still have a reel of Vantage 1 and a reel of Vantage 2 , only difference was blue stripe. I also have a reel of an amber nylon with a green stripe that I got from Bancroft Sporting goods, as I was a dealer years ago during the wooden era.
Nat. gut, Victor Imperial, and Bow brand was what I carried for years, was a little more expensive at $10.00/ set, as that typically came in 2-17' sections.
Once in a great while an old time hitter will have me string up one of his wooden racquets with one of those nylon strings.