Goood morning everybody.

Welcome Max!  Without the trim tag, you have limited options in finding the original color.  Your best chance (in my opinion) would be to check for the "tank sticker."  This is also known as the build sheet and was used by the factory to know what options to put on the car.  During assembly, it was typically glued to the top of the gas tank (hence the tank sticker name).  They have also been found under carpet, inside the dashboard, under or inside of seats and other places, but the top of the tank is probably your best bet.

What year is your car and what color is it now? Maybe look around under the hood and fenders and stuff to see if it was a different color before. What color is the interior? If it's a convertible, what color is the top? Maybe with more info people here can help figure it out for you.

Welcome to C3VR!
Are you talking about the actual, metal trim tag that is attached to the body at the front of the door jam, or the blue paper tag on rear edge of  the door itself?
If the metal trim tag is gone, it's going to be harder to determine the original color without the build sheet/tank sticker, but maybe not impossible.
Pull the carpet back from the sill plates, and look under there for evidence. These cars were originally painted with no trim/interior stuff, so the floors would have substantial overspray of the color. Most repaints do not go through the trouble of removing the interior and covering all of the original color. Also, the hood hinges may still have some of the original color on them, as they were on the car when it was painted.
You might take some of the interior trim pieces off, and see if there is a different color under them than what is on the car.
 As far as interior color, it's next to impossible to determine what it had originally without the trim tag, or build sheet, as the interior can be completely changed, with no evidence of the change in either color, or fabrics.
Do you think the car has had a color change, or are you just wanting to determine if the colors it has are original?

Joel is right.  The only thing I can add is that most replacement consoles and e-brake covers look like replacements if you take them apart and look.  If your seem original, you probably have the original color.  This can be a chance to make the car the way you want it.  Replacement trim tags are available with whatever information you want on them.

Larry

Thanks to all !!! I try to search in all the corners but nothing!!! I think to have find the original external colour,under 5 layers of paint,(blue,yellow,blue,orange,red) but not the interior. The previous owner spray black all the interior. I think the colour was dark saddle...is only my idea! I try to search on the web some book can tell me,if is possible, the combination of color (ext and int).

Max, car looks pretty nice, so it looks like it was blue. Are the corvettes liked over in Italy?

Looks like the car was originally blue...or at least the door you have the pic of was. There doesn't seem to be any overspray on the fasteners on that door, so...that's a good indication that blue is the original color. It would have been available with a saddle colored interior, too.

 The steering wheel appears to be from a '76.  That part seems to have been replaced.  The color looks to be BRIGHT BLUE.

Look at this web site.  It may tell you some interesting information.