– By ALAN SCULLEY

Indigo Girls — Amy Ray and Emily Saliers — have long been as famous for their differences as for their music. They even named their 2006 CD “Despite Our Differences.”

The contrasts show up both within and outside of their long-standing group.

Outside of Indigo Girls, Ray and Saliers lead pretty separate lives. Ray is known as the more outgoing of the two, and she and Saliers have fairly different interests.

For instance, Saliers owns a restaurant in Decatur, Ga. Ray, meanwhile, spends much of her time outside the group on her solo career. She has released three studio CDs of songs that rock harder and frequently have a punky edge — a sharp contrast from the folk-rooted, often acoustic-based pop that has been the signature of Indigo Girls since their 1987 debut, “Strange Fire.”

And while Ray and Saliers have always written their songs for Indigo Girls separately, over the years it’s become easier to discern which songs are written by who.

The contrasting writing styles are arguably more pronounced than ever on the brand-new Indigo Girls CD, “Beauty Queen Sister.” The different writing styles, obviously, aren’t news to Ray, but she agreed there is truth to that notion.

“I think the distinction may be growing,” she said. “And I think it’s because both of us have spent a lot of time on our writing now and have more of a discipline around it. So we’re just more of what we are I think that’s just a matter of getting older and feeling not a lot of pressure and just saying these songs are going to be radically different from each other, but it all works somehow.”

What’s becoming more apparent is that Saliers generally writes the songs with the widest appeal to the Indigo Girls audience and hews closer to pretty acoustic ballads and easy-going, mid-tempo material.

This time out, her contributions include “John,” “Feed and Water the Horses” and “We Get to Feel It All” — three mid-tempo tunes that are soft around the edges and filled with rich melody, and fit in the tradition of Indigo Girls hits such as “Closer To Fine” and “Galilelo.”

Ray, meanwhile, is growing into the more adventurous force within Indigo Girls’ songwriting equation.

On “Beauty Queen Sister,” she wrote the title track, which rides some chunky electric guitar to give the song some gentle punch, and “Making Promises” (the first single), an infectious pop-rocker spiced by slide guitar. “Damo,” meanwhile, gets a decidedly Celtic folk treatment.

“It’s just what it is,” Ray said. “I’m not really the hit writer. I’m kind of more the — I don’t know what I am — the rodeo clown, I guess, in some way. And I just, I think I’m a different writer from Emily and she’s, in some ways, her songs appeal to our audience on a wider kind of basis sometimes.

“But that frees me up a little bit probably to push the envelope, honestly, because I don’t have a lot of pressure to write (another) ‘Closer to Fine.’ I’m just writing the best song that I can. And sometimes it’s stepping out of the box a little bit, and that’s OK to shake it up a little bit. “

Fans, of course, don’t have to worry that Indigo Girls have morphed into something they won’t recognize. But the growing divergence between the songs Ray and Saliers write is helping to keep the duo a living and growing musical entity from album to album.

The greater contrast between the songs of Ray and Saliers, however, isn’t the only thing that might help set “Beauty Queen Sister” apart from the other 11 Indigo Girls studio albums.

The instrumental treatments also branch out in some new directions for the duo. A couple of songs — “Share the Moon” and “Able to Sing” — make greater use of keyboard textures within the group’s sound, using them as a bed below the vocals to enrich the sound.

Violin, meanwhile, is also featured more on “Beauty Queen Sister” than any other Indigo Girls CD, as the playing of Luke Bulla (who played on the duo’s 2010 Christmas CD, “Holly Happy Days”) adds layers of melody to songs such as “Yoke,” “Share the Moon” and “Birthday Song.”

Bulla isn’t touring with Indigo Girls this fall, but Ray and Saliers are adding to their acoustic guitars by bringing along a violinist and a keyboard/accordion player.

“We’ll probably play, I don’t know, 75 percent of the new record and then the other half of the set will be us singing old songs,” Ray said.

IF U GO

INDIGO GIRLS

WHEN: 8 p.m. Tuesday and Wednesday

WHERE: Jonathan’s, 92 Bourne Lane, Ogunquit

HOW MUCH: $82 in advance; $90 day of show

INFO: jonathansrestaurant.com