Since Dame Agatha was writing for 55 years first editions of later books came out the same time as hundredth edition of so of the first books.
Ten Little Negroes (or a word similar to that) is cyan (blue green) with red writing with a white hand picking up the black
figures. The US shows a bony figure pointing to an island. Agatha Christie is in red, highlighted in white. 1939
Murder on the Orient Express. The writing is in yellow. It says Agatha Christie in capitals and then in small writing "Poirot solves a" and in bigger writing "Murder on the Orient Express." It shows an engine driver and fireman on an anonymous steam train (it faces forward). 1934
Death on the Nile. The name and title are in capitals. It says "A Poirot story". There are two Egyptian god sculptures and the boat is at the bottom. 1937
The Mysterious Affair at Styles shows two characters in the dark. The man is in profile, the woman faces towards us. 1920
Murder of Roger Ackroyd has the writing in red. A girl in a yellow dress is stuffing paper into a drawer. There is a old fashioned telephone. 1926
The Body in the Library. The title words are made up of books highlighted in red. 1942. It was in fact published in the US first.
The Murder of the Vicarage has the writing in white with a red stencil outline. A policeman takes notes from a gentleman and a vicar (who else?) 1930.
The 4.50 From Paddington. All writing is in shaky white capitals. 'Agatha Christie' has a black background, the title has a red background and there are the words "Crime Club Choice' also with a black background. 1957
A Murder is Announced. The name is in yellow and capitalised. There is the writing "For the 50th time the Queen of Detective Novels defies her readers."* There is the bottom half of a clock under this, at half 6. And under this is the title. 1950
* Pedant alert! Actually it was her 49th book.
The ABC Murders. The title is in red, with a block ABC, the name is in italic and more slanted than usual. The background is a yellow ABC railway guide. 1936.