Modify Biblatex so citations appear as (author, year: pagenos)

I am really struggling to find a way to modify biblatex authoryear so that it comes out in this modified Harvard style. In case any solution can be helpful to others in the future, this is the style Sage Journals request.

What I want: (author, year: page).Biblatex author year normally produces something like this: (author year, page). By page, I mean the page in the cited document with the referenced material.

Here is a sample bibtex reference and how I would like it to apprear:

    @book{Varshney:2003tn,
author = {Varshney, Ashutosh},
title = {{Ethnic Conflict and Civic Life}},
publisher = {Yale University Press},
year = {2003},
series = {Hindus and Muslims in India},
isbn = {9780300100136},
language = {English},
date-modified = {2012-12-14T03:45:28GMT}}


In-text citation:

    Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua (Varshney, 2003: 83-85).


Bibliography Entry:

    Varshney, Ashutosh. (2003) *Ethnic Conflict and Civic Life: Hindus and Muslims in India*. Yale University Press.


Any help is much appreciated!

EDIT: Included an example!

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Welcome to TeX.sx! Please add a minimal working example (MWE) that illustrates your problem. – Guido Jan 7 '13 at 11:31
Is the pagenos, the page number of the citation (and it would not make sense for a book), or the page number where the material specific to the citation appears. If this is the case, then you can use \cite[pagnos]{citekey}. – Guido Jan 7 '13 at 11:34
Thanks for the replies. I mean the page number of content being referenced (sorry for the confusion). – Michael Davidson Jan 7 '13 at 16:24
I've added an example which will hopefully make it clear. – Michael Davidson Jan 7 '13 at 16:25
Could you explain how this differs from what you currently get with your preferred bib style? – Seamus Jan 7 '13 at 16:32

In general, see Guidelines for customizing biblatex styles. In your specific example, don't capitalize "english" in the .bib file.

\documentclass{article}

\usepackage[english]{babel}

\usepackage[style=authoryear,isbn=false]{biblatex}

\DeclareFieldFormat{postnote}{#1}
\DeclareFieldFormat{multipostnote}{#1}

\usepackage{xpatch}
\xapptobibmacro{date+extrayear}{\nopunct}{}{}

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@book{Varshney:2003tn,
author = {Varshney, Ashutosh},
title = {{Ethnic Conflict and Civic Life}},
publisher = {Yale University Press},
year = {2003},
series = {Hindus and Muslims in India},
isbn = {9780300100136},
language = {english},
date-modified = {2012-12-14T03:45:28GMT},
}
\end{filecontents}

\begin{document}

Some text \autocite[83--85]{Varshney:2003tn}.

\printbibliography

\end{document}


Note: I didn't tinker with the formatting of the series field; in your "Bibliographic Entry" snippet, "Hindus and Muslims in India" (italic, colon prepended) resembles a subtitle rather than a series title.

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Thank you! This is great and I think I am beginning to understand how to edit the biblatex formatting. – Michael Davidson Jan 7 '13 at 18:44