From Keith Tanner’s book “Mazda MX5 Find it fix it trick it” ( a fun read and worth buying if you can find it cheap) , 18P means
1 - two wheel drive
8 - convertible body style
P - engine code ( 1.8 litre)
The VIN does not contain any info on paint colour and as far as I know there is no paint code indicator on the car itself. Assuming the car is in its original colour, it is Strato Blue Mica 25E as that is what was offered in the January 2004 UK brochure (and it looks like the colour in the brochure pics). Your car appears to be a 2004 or later build, as it has the silver-painted centre console trim and windblocker speakers which were standard on 1.8 litre models in the Jan 2004 brochure. Before that the silver trim was not available, windblocker speakers were only fitted to the Euphonic and the blue was Supreme Blue Mica 22A, which looks too light in the 2003 brochure pics…although it is not easy to tell!
You could try going to the Parts department of a Mazda Dealer and ask them for something, they will ask for the VIN to put into the parts system and that should bring up full details of the car, including the original paint code.