Despite the 1934 date, yellow-seal bills were actually printed during WWII for use by troops in North Africa. More than one denomination was issued; please see the following questions: "What is the value of a 1934 US 1 dollar bill with a yellow seal?" "What is the value of a 1934 US 5 dollar bill with a yellow seal?" "What is the value of a 1934 US 10 dollar bill with a yellow seal?"
The seal color is actually yellow but has darkened with age. Yellow-seal bills were printed for use by troops in North Africa during WWII. There's more information at the question "What is the value of a 1934 A US 10 dollar silver certificate with a yellow seal?"
Despite the 1934 date, yellow-seal bills were actually printed during WWII for use by troops in North Africa. More than one denomination was issued; please see the following questions: "What is the value of a 1934 US 5 dollar bill with a yellow seal?" "What is the value of a 1934 US 10 dollar bill with a yellow seal?"
Please check again and post a new, separate question.There were no 1926-dated US bills.There were no orange-seal bills.The US did print yellow-seal $1 bills but these were dated 1935A.
A 1928 $5 US Note should have a red seal, although it's possible the original color has changed due to time and/or exposure. If the seal is definitely yellow, please check your bill and post a new question. The only small-size $5 bills with yellow seals were dated 1934 and were printed for use during WWII.
Please check your bill again and post a new, separate question. A red seal would indicate that the bill is a United States Note, but 1934 A $5 bills were printed as green-seal Federal Reserve Notes and blue-seal silver certificates. There were also yellow- and brown-seal bills with that date printed for use during WWII.
Please check the date again. There were no 1968 US bills and the last red-seal $5 bills were dated 1963.
There haven't been any blue-seal $20 bills issued since 1918. You may be seeing the blue underprinting of its background, or the bill may have been exposed to something like laundry detergent that affected the seal's green ink by removing some of its yellow component.
These bills were dated 1934 rather than 1943. Please see the Related Question for more details.
All US $100 bills printed since 1969 have been Federal Reserve Notes with green seals. The last blue-seal $100 bills were dated 1918. It's possible your bill was exposed to a chemical that changed the ink's color. Some strong detergents have been known to alter the blue/yellow balance in the ink used for the seal and serial numbers. You'd need to have it inspected in person to be sure, though.
There were never any $1 gold certificates. All 1935-dated $1 bills were silver certificates. However some 1935 A bills were printed with yellow seals for use by troops in North Africa. If your bill has the words NORTH AFRICA overprinted on its back, please see the question "What is the value of a 1935 A US 1 dollar bill with a yellow seal?" for more information.
Please check your bill again and post a new, separate question. 1928 US $1 bills were issued as red-seal US Notes or blue-seal silver certificates. The first green-seal $1 bills weren't printed until 1963.