Weird LSCOLORS after copying files
The filesystem on the external storage device does not have a sense of Unix permissions. For example, the external drive may be formatted as one of the FAT variants of filesystems. When you copy the file from the external storage to the Mac's hard drive, it copies the permissions as they were found on the external drive.

Use the idea below or variants of it change the permissions back to something standard on a Unix filesystem. Below, change all files in ~/Pictures with the extension, png, to 0644 (owner = read write, group = read, others = read) and  directories to 0755 (owner = read write execute, group read execute, other = read execute). In context of directories, execute provides the ability to change directory (cd) into the given directory. These are typical, default permissions.

find ~/Pictures -type f -name '*.png' -exec chmod 0644 {} +
find ~/Pictures -type d -exec chmod 0755 {} + 


The type option, above, takes an abbreviated file type argument; f specifies regular files, and d specifies directories. The -exec option specifies what to do with found files. In this case, we want to "change mode" (chmod or change permissions). The {} is a list of found files. 
Use man find and man chmod for more information. Another nice resource for Unix commands is explainshell.com. 

Some of the files may require the execute bit. For example, if you have a script that you want to execute directly, use something such as the following (owner = read write execute, group = read execute, others = read execute).

chmod 0755 script.sh


The permissions above are written in octal notation. Wikipedia has a nice summary of the meanings. After getting the permissions back to normal, the colors can provide the right visual hints again.