Start with what you're presenting. 8.5"×11" fits standard letter documents, certificates, and most everyday prints — it's the size to default to when you haven't been told otherwise. 11"×14" is a classic photographic print and mat size, suited to portfolio and gallery-style presentations. 11"×17" is tabloid size, right for design layouts, comps, and architectural sheets that need more room than letter paper. 13"×19" is Super B — the largest sheet size most wide-format inkjet printers handle — built for photographers and printmakers who want their large-format prints to go straight into the page at full size.
For color, black and silver are the neutral, professional choices for client meetings and interviews — black keeps attention on the work, silver reads a little more contemporary. Red and blue suit two different jobs: standing out when the portfolio itself is part of the impression, or color-coding a set of books by client, project, or class. All four colors and all four sizes use the same archival sheet protectors, so the choice is about presentation and organization, not capacity — every book starts at 10 pages and can be topped up to 15 with matching refill pages.