The novel certainly goes from dark to light physically, mentally, and emotionally! With the image of the rooms where the people sleep being completely white contrasted with the candles used at night and Equality's cave, it would seem like this book would be perfect if shot as a black and white movie. Then, just like the Wizard of Oz, the movie version could change into technicolor when he escapes to the forest. That being said, the word "blacker" is appropriately placed within the first paragraph of chapter one. In Signet's student edition, the story begins on page 18 and Equality is already in the cave writing his first entry which says:
"It is a sin to write this. It is a sin to think words no others think and to put them down upon paper no others are to see. It is base and evil. It is as if we were speaking alone to no ears but our own. And we know well that there is no transgression blacker than to do or think alone."
So, yes, the first image is the word "blacker" coupled with "transgression" or "sin" which starts the book off in a very dark mood.