junction table
------------
car.....color
1........1
1........2
1........3
2........1
3........2
3........1

if one car can be as much as 3 colors does the above junction/composite table violate anything is it the right way to approach it?

All kosher, but if you are LIMITING cars to a maximum of three colors, you will need additional constraints.

alrighty thanks, I might need to research these constraints up.

create table junction
( car integer
, colour integer
, seq tinyint
, check ( seq in (1,2,3) )
);

not sure what the PK would be, though... blindman?

Why make every column nullable?

At least you'll need a uniqueness constraint on (car,seq) otherwise it would still be possible to have more than three colours per car. It also seems sensible not to allow the same colour to appear twice per car. I'd expect referential constraints too:

CREATE TABLE CarColours
( car INTEGER NOT NULL REFERENCES Cars (car)
, colour INTEGER NOT NULL REFERENCES Colours (colour)
, seq TINYINT NOT NULL
, CHECK ( seq IN (1,2,3) )
, UNIQUE (car, seq)
, PRIMARY KEY (car, colour)
);

I'm not a fan of primary keys and I'm not stating an opinion about which key is the "primary" one or even whether it matters at all. Not to be too controversial though, I've included a PRIMARY KEY constraint anyway.

You're not a fan of primary keys?

I think you should go stand in the corner and think about what you just said for a moment.

Lol! I think dportas might actually have some interesting points to make on this. I suspect his thinking is with regard to relational purity and (IIRC) Codd shoe horning PKs in as a late revision. There are a few that don't like the concept of PKs, saying they are just a hang over from, and concession to, technical standards that predate Codd's work.
I very much doubt he is bemoaning constraints enforcing uniqueness.

pootle flump ur codings are working excelent.

Seems a very small number of colour options for a car or has the US gone back to Henry Ford's original colour schemes for the model T? I know my old VW beetle comes in 17 colours for 1972 alone - my one is currently blue.

Comment removed due to my misunderstanding.

Mike - the requirement is 3 colour combinations per car.

EDIT - more accurately, a combination of three colours per car....

pootle flump ur codings are working excelent.

To clarify; 3 colours per car, not per model... right?

Further clarification as I understand it:
Each physical instance of a car (i.e. a tangible object that can be used to transport people and other matter from one place on earth to another, and not a theoretical construct such as a "model") can be coloured by up to three colours from a domain of available colours. I imagine each car must have at minimum one colour, otherwise it would be a magic car, but this has not been stipulated as part of the requirement.

pootle flump ur codings are working excelent.

The DeLorean didn't have colours - it was just sheet steel - or does that count as a colour.

Magic?
Or transparent!

So we're talking about: car registration "UB3R FLMP" comes in yellow, red and blue. Yellow body, red dash and blue upholstery.

In which case, is the colour not an attribute of the car part rather than the car itself?

wanted to illustrate only the CHECK constraint in the seq column

to include the FKs, and do a thorough job of it, would require that i ensure that the columns that the FKs reference also existed properly, which would mean i'd have to give the DDL for the cars and colours tables, too, and i couldn't be ***ed this time

I wouldn't enforce this using a Sequence column.
I'd enforce it using an indexed view, though that is an MSSQL specific solution.