Can you explain why some US notes have different colored seals? Do these notes have a high numismatic value?
One answer isn’t going to fit all of your questions. In the early days the size and color of the Treasury Seal on notes varied greatly, as did the colors. In general they changed colors to thwart counterfeiters and to differentiate between series of notes.
To determine what kind of a note you have, look at the wording above the central portrait. The most common note in circulation today is the “Federal Reserve Note.” You will find that the seal color is green. Following is a listing of other 20th Century US notes that you may find in circulation or at numismatic sales or events:
Silver Certificates— Blue Seal
US Notes— Red Seal
National Bank Notes— Brown Seal
Gold Certificate— Yellow Seal
The numismatic value of paper money is based on rarity and condition. While early issues of “large-size” notes may hold numismatic value in various conditions, the enormous quantity of issues during the 20th Century dictate that few “small-size” notes will attain a significant numismatic value in less than uncirculated condition. If your note is in crisp, uncirculated condition you may want to seek the advice of a local numismatic expert.