I've only seen a Lemans RS in that color, and only one.

However, I think it's an '86 or '87.
Those look like the Panaracer tires that came on it, though.
If those rims are Wolbers, I'd say '86
If those rims are Araya's, I'd say '87
The reason I don't think '88 is the grouping would, I think, be Shimano 600 tri-color.

If the SN says '88, then it is a rare bird, probably the very early production run.
The '88's had a different Tange 1 sticker.

If that's an '86, you've got a rarer one than the red/white '86, mainly due to color.
It's a gem, and I'm glad it fits you.

If you need anything for that bike that I have, just let me know.