Perspicuity probably isn't gonna be a terribly popular word in the Catholic world. The Catholic Church doesn't hold any scripture to be self-interpreting, not even the things that seem obvious; this is a safeguard to preserve one authentic teaching authority of the Church.
In a document promoting unity between Christian Churches in the 1970's this difference was pointed out between all denominations started after the Reformation:
In the history of the Church, the difference between Catholics and Reformed has always focussed on the alternative: “Scripture and Tradition” and “Scripture only”. Catholics stressed the need for and the authority of the Church’s teaching office in the interpretation of Scripture, whereas the Reformed declared that Scripture interprets itself and, as God’s Word, must be strictly distinguished from all human tradition, desiring in this way to do justice not only to the doctrine of justification but also to the total witness of the Old and New Testaments.
THE PRESENCE OF CHRIST IN CHURCH AND WORLD
and also, a difference between Evangelicals and Catholics in particular:
Evangelicals acknowledge the wisdom of listening to the Church and its teachers, past and present, as they seek to understand God's Word, but they insist that each believer must be free to exercise his or her personal responsibility before God, in hearing and obeying his Word. While the Church's interpretations are often helpful, they are not finally necessary because Scripture, under the Spirit's illumination, is self-interpreting and perspicuous (clear).
Thus, contemporaneity has come to mean different things in our two communities. Each recognizes that the Word of God must be heard for and in our world today. For Roman Catholics God's Word is contemporary in the sense that it is heard and interpreted within the living Church. For Evangelicals it is contemporary in the sense that its truth has to be applied, by the illumination of the Holy Spirit, to the modern world.
THE EVANGELICAL-ROMAN CATHOLIC DIALOGUE ON MISSION, 1977-1984
Catholics have always held there to be three pillars, Sacred Scripture, Sacred Tradition and Magisterial Teaching. These three in concert comprise the deposit of Faith. I don't think you'll find evidence to the contrary in the Middle Ages or before about scripture being easy to read. Then, it was definitely up to the Priests to interpret. Passion plays and art were a perspicuous witness to the Gospel, but so were Priests, just like the Apostles were before them.
And the idea that Sacred Scripture is so easy to understand that any dummy can do it is shown as unbiblical by the Bible itself. When Philip popped down for a visit in Ethiopia, the eunuch (who was probably no dummy) said. "How can I understand what I'm reading (talking about Isaiah) unless some man shows me" (Acts 8:31). And St. Peter says that teachings are hard to be understood by the unlearned and the unstable - and they interpret them to their own destruction (2 Peter 3:16). Hopefully, I'm not misinterpreting that.
Even here, Catholics are wise to say that this is "just my opinion" of sacred scripture (even though I pulled it right out of "A Textual Concordance of the Holy Scriptures") because we don't have any teaching faculty in the Church.
