я честно говоря в атарях не-разбираюсь.
(xe продал поскольку почти не-было софта, ST лежит на антресолях).
The operating system also maintains copies of these color registers in RAM memory. These are called shadow color registers. They are maintained because the hardware locations are "write only" locations. Since they can't be read, we need RAM locations where they can be read. At the beginning of each refresh cycle, these five shadowed registers are copied into the hardware locations.