Spanish language Q&A Forum

Hi there, I am a little confused as there appears to be inconsistencies in the colouring of letters which are irregular in the verb tables.
In this table only the Z is red, I understand that the letter Z is the main focus of the lesson, however almost all of this verb is irregular, and only highlighting the Z makes me question myself.
In other lessons I have seen emphasis with both red and blue, but there doesn't appear to be a regular pattern, which also casts doubt on my learning.
I know it may be a big job, but would it be possible to devise a standard practice, and then implement? Maybe a job for a Spanish intern :-)

In the first sample sentence above, what is the function of 'lo'? There are 4 such examples on this page.

Didn't we learn in another lesson that we could substitute "que" for "porque"? Does that mean "debido a que" and "que" are also interchangeable via the transitive property? I feel like either I am misremembering or there are some nuances I'm not picking up on. 

Just a suggestion:  I feel that the question set for this lesson could be more challenging.  Could add 4 or 5 questions with more room for error rather than translating from Spanish to English.  Choices in Spanish where we could easily go wrong.