I don't Know about current M113 in the US But if I remember correctly NAm Versions were a light pale green and so were Israeli versions.I've always used Tamiya XF-21 "sky" for M113 interiors.

Go to my motorpool album (AFV References, Modern, US) and you will see the inside of M113/BFV FOVs in the infamous "seafoam green".

I've seen several postings on this very same issue.
It seems that (glossy?) white has been used briefly in the seventies, but sea-foam is most certainly in fashion today. Same applies to many other AFV"s

The closes FS I found for this color is FS 34424.
I have always used Polly S or Polly Scale 505254 Sky Type S for this color. I once brought a bottle of this color to guard drill and painted a patch on the interior of one of my M113A2s. While it is slightly lighter, which I accont for as scale lightening, the color tone is quite a good match.
It's slightly darker that the underside color of the RAF Day Fighter Underside color. So the use of Tamiya Sky is quite acceptable.
Other mathes include Humbrol 23, Lifecolor UA095, Gunze H74, Modelmaster 4840 and Xtracolor X7.

White is still used on the interiors of tanks and other closed topped AFVs. It helps keep the crew from going nuts (some kind of psychological thing). The green is used as an interior color for infantry type vehicles with larger open hatches and loading ramps. Supposedly it is light enough for the psychological benefit, but subdued to reduce external observation...the white contrast would be really noticable in the field. #:-)

All the M113 interiors I remember in 'NAM were white. The only variations I recall were the mortar tracks, where the driver's compartment was the seafoam color and the fighting compartment was an olive green color. Also the M132 flamethrower tracks had a seafoam color interior. As someone else posted, the Polly S British sky color is a great match for the seafoam green color used today.

I use to use "Duck Egg Blue" an old RAF color, I believe is now called "Sky". We used "Gloss White" inside our tanks as it had best light reflection and made the inside "look" as big as possible #:-) God, how I hated to button-up

I recall the original name for the color was Duck Egg blue...As my dad did alot of RAF and RN aircraft, I became familiar with it.

I use Humbrol sky as well. Its as close as I can come to with actual comparison to the real thing. The maintainers thought I was nuts when I actually painted a little dab on the inside of a track to compare the shades!