Learn English – Modal verbs + be + past participle

if you tried ... you would ... find ...
if ... you began ... you would ... have laid up ...

Both of these woulds represent future constructions cast into past form to agree with the 'hypothetical' past form in their respective if clauses. They might with perfect propriety be expressed using present forms:

if you try ... you will ... find ...
if ... you begin ... you will ... have laid up ...

To which you might revert is a present form with future reference, again cast into the past form to express hypotheticality. Its Event time is its main clause’s Reference time, in a few years. Once more, all of these could be expressed with present forms:

if from [NOW] you begin ... to correct your thoughts and actions, you will in a few years have laid up a new and stainless store of recollections, to which you may [AT THAT FUTURE TIME] revert with pleasure.

Jane, however, is careful to keep her moralising in the hypothetical mode, whether because she is reluctant to instruct too directly an older and far more sophisticated man, who is moreover her employer and social superior, or because she is “sensible that the character of my interlocutor was beyond my penetration; at least, beyond its present reach; and feeling the uncertainty, the vague sense of insecurity, which accompanies a conviction of ignorance.”

Technically, the tense should match, so since we're using the perfect tense (conditional perfect in fact), you should use was.

But both could have ... is and could have ... was are acceptable in this case.

Why? Well, it's because your clause about the paprika being similar to the bell pepper might be true for a long time, and might continue to be true even in the present, so it might be okay to use is.

Maybe not. Maybe the paprika is rotten by now, or already eaten. Then is would make no sense. But a situation continuing to the present would justify use of the present tense is.

Consider:
"I could have gone shopping, because the supermarket was near."
"I could have gone shopping, because the supermarket is near."

If the supermarket has not suddenly moved, it probably still is near – it is now, and it was then – so either one is acceptable.

But some things do not last so long:
Correct: "I could have stayed longer, because it was early in the morning."
Incorrect: "I could have stayed longer, because it is early in the morning."

Unless you are describing something in the very recent past (minutes or hours ago), the fact that it is now early probably has nothing to do with the situation in the first half of that sentence, so mixing the past and present tense in this last example doesn't really work.