I agree with Barry, you need to give us a little more information.
How many keys do you need, to some extent that decides the kind of keypad you need?
3x3 or 4x4 (2 models)
Are the sounds complex (like chimes/ringing/something recorded) or just plain beeps at different pitches?
The sounds are phrases (hello, how are you?)
Does a key press produce just one sound when held down or should there be a sequence of sounds triggered by a single press?
One sound.
The biggest single item in the enclosure will probably be the loudspeaker, how loud does it have to be?
How can i measure it? (5 meters without distorsion)
As for colors, I use cheap 4x4 membrane keypads like these:
https://www.ebay.co.uk/itm/4x4-16-k...775430&hash=item3d70d80c8b:g:JcAAAOSw2BFdKFdh
then use a color laser printer (inkjet works just as well) on a sticky packaging label to make an overlay for them so they look like this:
View attachment 154968
Finally, I aerosol spray the label with a fixer, the kind you use on inkjet prints to make them glossy and more durable. The one in the photograph has had about five years use.
Regarding the keypad, I do not think the membrane keypad will be a good option for an old lady (better buttons).
Brian.